问题
选择题
It never _____ humans until the mid1990s that some animals can be cloned.
A．occur
B．is occurred
C．occurred to
D．occurred
答案
答案：C
题目分析：It occurs to sb that 某人突然想到...，occur to 发生，突然想到。。。句意：直到20世纪中期人类才突然想到克隆出一些动物。
点评：注意句型的识记。
