He ran off____ I could stop him.

A. before             B. after          C. since          D. when

They had camped once before, ____ they knew what to take.

A. because         B. now          C. so              D. since

Go ____ the gate and you' 11 find the entrance ____ the park ____ the other side.

A. through; to; on B. along ;of; on  C. down; to; at     D. up; of; by

He is running ____ the wind towards the east of the station ____ Tom is running ____ the right.

A. down; and; on B. against; while; on C.for;with;in     D. with; while; to

He wrote the article ____ three days.  

A.at                       B.in                           C.on             D.by

Mary dropped in ____ Mr Smith, but he  wasn' t at home, so she went to drop in ____ Mr Smith's office.          

A. on, on         B. at, at          C. on. at          D. at. on

1 feel that one of my main duties ______ a teacher is to help the students to become better learners.

A. for                  B. by               C. as                D. with

Go back ___ you came from.    A. until       B. where       C. which        D. when

We can surely overcome these difficulties _,___ we are closely united.

A. so far as               B. so long as              C. as soon as           D. as well as

The two rings are so alike that it is difficult to tell one the other．

A．very；to B．much；to C．much；from D．very；from