yesterday afternoon the children went out to saw the tower being erected in the park

问题描述:

yesterday afternoon the children went out to saw the tower being erected in the park
为什么不是erected?

可能这句话想表达的意思是:一直耸立在park的tower,being表示的是一个持续的状态,从过去持续到现在;而不加being,表达的侧重点是已经坐落在park的tower.