1. I heard someone the piano in the next room when I walked past it.

A.play
B.playing
C.to play
D.to playing

B

根据题意“当我走过时，听见某人正在隔壁弹钢琴”，hear sb. doing sth. 表示听到某人正在做某事，强调动作正在进行，符合题意。而hear sb. do sth. 表示听到某人做某事的全过程，不符合语境。没有hear sb. to play/to playing的用法。所以此处应填playing。

2. He was seen football on the playground yesterday morning.

A.play
B.playing
C.played
D.to play

D

本题考查感官动词看（see）的被动语态用法。在主动语态中，see sb do sth（看见某人做某事全过程）和 see sb doing sth（看见某人正在做某事）。而在被动语态中，要还原 to，即 be seen to do sth。此句表达的是昨天早上有人看见他在操场上踢足球，强调看到动作的全过程，所以用 be seen to do sth 结构。

3. The mother watched her son (cross) the street and (disappear) into the crowd.

cross; disappear

1. [2024·连云港] The past can never be changed and it is (use) to worry about the future. Why not enjoy the present?
2. [2024·达州] It is (luck) for us to be born in China.
3. With the development of modern transportation, it's easy for us (travel) around the world now.
4. 你真是太好了，帮我解决了这个数学问题。
It's very you me with this math problem.

1. useless；
2. lucky；
3. to travel；
4. kind； of； to； help。