1.falling.see sb doing sth 看到某个动作的一部分/或看到该动作正在进行
2.pick up have sb do sth 让某人做某件事情
3.filling; hidden 因为 tears fill his eyes(习惯用主动）,the words are hidden in his hear（习惯被动） 所以答案为filling和hidden.
4.fixed 因为sb fixe his eyes on the ceiling,因此eyes与fix的关系是被动的.