选A "当我看见那些我小时候就熟悉的建筑被拆迁走的时,我感到有点低落."
先来分析一下这个句子：I(主语) was(谓语) a little disappointed(表语) when I saw the old buildings(时间状从) 【that I had known as a young boy(定从,修饰"buildings")】 were now gone.把括号内容删去,剩下：I was a little disappointed when I saw the old buildings were gone.这题就很简单了,考的是词组"see sth.be done"(看见某物被.).选A.