List of top Verbal Reasoning Questions on Critical Reasoning asked in GRE

People whose bodies cannot produce the substance cytochrome P450 are three times as likely to develop Parkinson's disease, a disease that affects the brain, as are people whose bodies do produce this substance. Since cytochrome P450 protects the brain from toxic chemicals, toxic chemicals probably play a role in the development of Parkinson's disease.
Which of the following, if true, most strongly supports the argument?
The early universe contained only the lightest elements, hydrogen and helium. Heavier elements, such as carbon, form only in nuclear reactions in stars and are dispersed when the stars explode. A recently discovered gas cloud contained carbon several billion years ago, when the universe was no more than two billion years old.
If the statements above are true, which of the following must, on the basis of them, also be true?
Soft Drink Manufacturer: Our new children's soft drink, RipeCal, is fortified with calcium. Since calcium is essential for developing healthy bones, drinking RipeCal regularly will help make children healthy.
Consumer Advocate: But RipeCal also contains large amounts of sugar, and regularly consuming large amounts of sugar is unhealthful, especially for children.
In responding to the soft drink manufacturer, the consumer advocate does which of the following?
Over a period of several months, researchers attached small lights to the backs of wetas—flightless insects native to New Zealand—enabling researchers for the first time to make comprehensive observations of the insects' nighttime activities. Thus, since wetas forage only at night, the researchers' observations will significantly improve knowledge of the normal foraging habits of wetas.
Which of the following is an assumption on which the argument depends?
Counselor: Every year a popular newsmagazine publishes a list of United States colleges, ranking them according to an overall numerical score that is a composite of ratings according to several criteria. However, the overall scores generally should not be used by students as the basis for deciding to which colleges to apply.
Which of the following, if true, most helps to justify the counselor's recommendation?
A thorough search of Edgar Allan Poe's correspondence has turned up not a single letter in which he mentions his reputed morphine addiction. On the basis of this evidence it is safe to say that Poe's reputation for having been a morphine addict is undeserved and that reports of his supposed addiction are untrue.
Which of the following is assumed by the argument above?
Adelle: The government's program to reduce the unemployment rate in the province of Carthena by encouraging job creation has failed, since the rate there has not changed appreciably since the program began a year ago.
Fran: But the unemployment rate in Carthena had been rising for three years before the program began, so the program is helping.
Which of the following, if true, most strongly counters Fran's objection to Adelle's argument?