实验结果表明，若以20岁时所需的照度为标准，则40岁为其（）
A.1.5倍
B.2.5倍
C.5.5倍
D.7倍多
参考答案：A
-种杀虫剂是由药粉和水按3：100的比例配成的，要配制515千克杀虫剂，需要药粉和水各多少千克？（用比例知识解）
— Has Tom finished writing his essay today?
— I have no idea. He ______ it this morning.
A．wrote
B．has written
C．was writing
D．had written
