用括号内所给单词的适当形式填空
1. I_______ (drop) the cup on the floor by accident.
2. They are _______ (possible) tired after working so long.
3. He tried many times and ________(final) he succeeded.
4. Fred is afraid of _______(fly). He feels anxious before he gets on the plane.
5. The bicycle must be ________(Carla).