Miss Gao often advises we should search for some on the Internet about science．（ ）
| A． |
instruction |
B． |
introduction |
| C． |
information |
D． |
invention |
I think it's impolite _______ others waiting．（ ）
A．to keepB．keepingC．keep
I cleaned my room yesterday． It _______ a little difficult．（ ）
A．isB．wasC．will be
Mountain climbing is one of _______ sports in the world．（ ）
A．dangerousB．more dangerous
C．the most dangerous
Are these your books？
No， they aren't． They are _______．（ ）
A．sheB．hersC．her
What's this？
It's _______ watch．（ ）
A．aB．anC．the