1. This experiment turned out to be _______ failure, but as we know, success often comes after _______ failure.
A. a; a B. 不填；不填 C. a; 不填 D. 不填; a
2. ----- Is Bob still performing?
----- I’m afraid not. He is said _______ the stage already as he has become an official.
A. to have left B. to leave C. to have been left D. to be left
3. You can’t imagine what difficulty we had ___________ home in the snowstorm.
A. walked B. walk C. to walk D. walking
