It will be three days he back from his home town..A. when; will comeB. after; will comeC.

问题补充：

It will be three days he back from his home town..

A. when; will come

B. after; will come

C. since; comes

D. before; comes

答案：

A. when; will come

B. after; will come

C. since; comes

(答案→)D. before; comes

解析：考察固定句式和时态。固定句式：It be 一段时间 before…一段时间以后某事才发生；如果before后面使用一般现在时，前面的主语使用将来时；如果before后面使用一般过去时，前面也使用一般过去时；本题前面使用了will，后面before后面的时态使用一般现在时。句意：三天以后他才从家乡回来。故D正确。