--What are you doing? ---- I am _____ a letter.
A.sending B. writing C.Both A and B
What is ____ envelope?
A. a B.an C ./
We put the address on _____ right.
A.a B.an C.the
There is a map________China ________the wall
A.of；on B.of；in C.of；behind
------I′m hungry。
-----Here is some bread ____________you。
A.to B.for C.of