标题: 请教一个时态问题 [打印本页] 作者: merrylili 时间: 2003-6-6 00:08 标题: 请教一个时态问题 (The domesticated camel, which some scholars date) around the twelfth century B. c., was the key to teh development of the spice trade in the ancient world.
D. the domestcation of the camel, thought by some scholars to have occured
答案选D， 可是 around the twelfth century B.C. is past tension, why use have occured?