1．(2011·上海市奉贤区质检)The exercises are extremely difficult but half of the class ________ them ahead of time.
A．has already finished B．will finish
C．have already finished D．finishes
解析：句意：这些练习非常难，但全班有一半的同学已经提前完成了。根据语境可知用现在完成时，排除B、D; the class 指全班同学为复数，故选C。
答案：C
