In October 1987 the United States stock market suffered a major drop in prices. During the weeks after the drop, the volume of stocks traded also dropped sharply to well below what had been the weekly average for the preceding year.
However, the volume for the entire year was not appreciably different from the preceding year’s volume.
Which of the following, if true, resolves the apparent contradiction presented in the passage above ？（）

A．Foreign investors usually buy United States stocks only when prices are low.

B．The number of stock buyers in 1987 remained about the same as it had been the preceding year.

C．For some portion of 1987, the volume of stocks traded was higher than the average for that year.

D．The greater the volume of stocks traded in a given year, the lower the average price per share on the United States stock market for that year.

E．The volume of stocks traded rises and falls in predictable cycles.

A与B之间的买卖合同是否成立，该画的所有权何时转移