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Jonas Salk is the American physician and medical researcher who developed the first safe and effective vaccine for poliomyelitis. Salk received his M.D. in1939 from New York University College of Medicine, where he worked with Thomas Francis Jr., who was studying how to develop vaccines from killed viruses. Salk joined Francis in 1942 at the University of Michigan School of Public Health and became part of a group that was working to develop a vaccine against influenza.
In 1947, Salk became associate professor of bacteriology and head of the Virus Research Laboratory at the University of Pittsburgh School of Medicine, where he began research on poliomyelitis. Working with scientists from other universities in a program to classify the various strains of the polio virus, Salk corroborated other studies in identifying three separate strains. He then demonstrated that killed virus of each of the three, although incapable of producing the disease, could induce antibody formation in monkeys.
In 1952, he conducted field tests of his killed-virus vaccine, first on children who had recovered from polio and then on subjects who had not had the disease. The results of both tests showed that the children’s antibody levels rose significantly and no subjects contracted polio from the vaccine. His findings were published the following year in the Journal of the American Medical Association.
In 1954, a mass field trial was held, and the vaccine, injected by needle, was found to safely reduce the incidence of polio. On April 12, 1955, the vaccine was released for use in the United States. Salk served successively as professor of bacteriology, preventive medicine, and experimental medicine at Pittsburgh, and in 1963, he became fellow and director of the Institute for Biological Studies in San Diego, California, later called the Salk Institute. Among many other honors, he was awarded the Presidential Medal of Freedom in 1977.
- What is the main idea of the passage?
- Which of the following is the closest in meaning to the word “vaccine” as used in line 3 of the passage?
- In the first paragraph, what was Thomas Francis Jr. studying?
- Which sentence in the second paragraph describes Salk’s first work at the University of Pittsburgh?
- Which word is closest in meaning to the word “corroborated” as used in line 22 of the passage?
- All of the following statements about the killed virus vaccine are true EXCEPT:
- Look at the word “findings” in line 35, Which of the following words or phrases from the previous sentence does the word “findings” refer to?
- From the passage, it can be inferred that the experimental polio vaccine was given to people by
- In the passage, it is implied that the Salk Institute was
- Where in the passage could the following sentence best fit?
“Thousands of children and adults were free from the fears of contracting this terrible disease.”CorrectIncorrect
The Missouri River is the longest tributary of the Mississippi River, and it begins its trip to join the Mississippi in the Rocky Mountains in Montana. The Missouri flows eastward to central North Dakota, where it turns southward across South Dakota, Nebraska, and Iowa. When it reaches Missouri, it turns eastward at Kansas City and meanders across central Missouri to join the Mississippi River, about 10 miles north of St. Louis, after traveling 2,315 miles.
Its drainage basin occupies about 529,400 square miles of the Great Plains. Elevations within its basin are extreme: from 14,000 feet above sea level in the Rockies near the Continental Divide to 400 feet where it joins the Mississippi. The flow of the Missouri changes frequently from 4,200 cubic feet per second to 900,000 cubic feet per second.
Its mouth was discovered in 1673 by the French explorers Jacques Marquette and Louis Joliet while they were canoeing down the Mississippi River. In the early 1700s, French fur traders began to navigate upstream. The first exploration of the river from its mouth to its headwaters was made in 1804–05 by Meriwether Lewis and William Clark. For many years, the river was, except for fur traders, little used by the earliest American settlers moving west. The American Fur Company began to use steamers on the river in 1830 but began to decline in the following year with the completion of the Hannibal and St. Joseph Railway to St. Joseph, Missouri.
For the first 150 years after settlement along the river, the Missouri was not developed as a useful waterway or as a source of irrigation and power. In 1940, a comprehensive program was started for flood control and water-resource development in the Missouri River basin.
The Fort Peck Dam is one of the largest earth fill dams in the world. The entire system of dams and reservoirs has greatly reduced flooding on the Missouri and provides water to irrigate millions of acres of farmland. Electricity for many communities is generated along the river’s upper course.
- In which state does the Missouri begin its trip to the Mississippi?
- Which of the following is closest in meaning to the word “meanders” as used in line 9?
- The passage implies that the elevation of the Missouri River’s drainage basin
- Which of the following is the closest in meaning to the word “mouth” as it is used in line 22?
- Where could the following sentence best be added to the passage? The speed of the river’s current is just as extreme.
- Who discovered the mouth of the Missouri River?
- When were steamers first used on the Missouri River?
- Which word does the word “power” as used in line 42 refer to?
- When was a flood control program for the Missouri River begun?
- In the passage, all of the following topics are briefly discussed EXCEPT: