Question

The visitors were surprised to see so many buildings going up at the same time.

为什么用going up形式

Answer 1

The visitors were surprised to see so many buildings going up at the same time.

参观者惊奇地看到，许多建筑物在同一时期拔地而起。

see .sb do /doing

do 原形表示看到全过程，
doing 表示看的时候，“正在做”；

显然，看不到全过程，而且，拔地而起，是进行意义。

Answer 2

表示现在进行时，看见一种状态。