[单项选择]Under D/P. all the documents, and usually title to the goods, are released to the buyer upon _____
A. his acceptance of the draft for payment at a specified later date
B. his payment of the amount specified under reserve
C. his partial payment of the bill amount
D. his payment of the amount specified

Passage Four
We all know that the normal human daily cycle of activity is of some 7-8 hours’ sleep alternating with some 16-17 hours’ wakefulness and that, broadly s peaking, the sleep normally coincides with the hours of darkness. Our present concern is with how easily and to what extent this cycle can he modified.
The question is no mere academic one. The ease, for example, with which people can change from working in the day to winking at night is a question of growing importance in industry where automation calls for round-the-clock working of machines. It normally takes from five days to one week for a person to adapt to a reversed routine of sleep end wakefulness, sleeping during the day end working at night. Unfortunately, it is often the case in industry that shifts are changed every week; a person may work from 12 midnight to 8 a.m. one week, 8 a.m. to 4 p.m. the next, and 4 p. m. to 12 midnight the third and so on. This means that no s
A. to change shifts at longer intervals
B. to have longer shifts
C. to arrange for some people to work on night shifts only
D. to create better living conditions for night workers