是cxcept还是except for?

先请看下列句子;①There was no one in the street____the policemen on duty.②The street Wit s e mpty____the policemenn on duty.③I know nothing about it____what 1 heard from you.④Everyone was right____me.以上四个句子的空白处,该用 except 还是 except for?这是初学者常常遇到的难题。正因为二者都表示“除……之外”的意思,初学者往往受汉语的影响而发生误用。要正确地使用它们,必须弄清它们在含义上和用法上的区别。