题目

已知a、b是两个自然数，若a+b=10，则a×b的最大值为（ ） A . 20 B . 21 C . 24 D . 25 答案：D 7．Schools across China are expected to hire 50,000 college graduates this year as short-term teachers __________increase job opportunities.        A．help  B．to have helped  C．to help      D．having helped