81. The question in the first paragraph is based on which of the following assumptions?

1. Direct observation is the only reliable method of conducting sleep research.
2. People will yawn most frequently in the moments before they fall asleep.
3. There is a direct correlation between yawning and sleepiness.
4. Yawning is a behavior over which individuals exert little conscious control.

82. The author mentions the "coffee break" (Line 3, Paragraph 4) to emphasize that ____.

1. a given attitude was inappropriate
2. a specific response was understandable
3. a particular action was unnecessary
4. a certain behavior was unexpected

83. The discussion of the "social aspect" (Line 1, Paragraph 5) most directly demonstrates ____.

1. the power of suggestion
2. a need for personal accountability
3. link between personality and behavior
4. the psychological cost of conformity

84. Which of the following, if true, would most directly disprove what "Scientists originally thought" (Line 1, Paragraph 6)?

1. Carbon dioxide does not affect people's breathing rates.
2. Yawning does not reduce the need for sleep, though it may make a person feel less tired.
3. Because yawning brings more air into the lungs, it can increase the rate at which oxygen is absorbed.
4. People do not tend to yawn much at high altitudes, where oxygen levels in the air are low.

85. The first sentence ("Since ... sleepiness") in the last paragraph primarily serves to ____.

1. introduce a lighthearted digression
2. provide a transition to a new subject
3. offer evidence in support of a prior claim
4. return the discussion to a problem mentioned earlier in the passage

(Reference keys.)