这个is / was不好辨

请看下面一道题：

He has changed a lot. He _________ not what he _________.

A. is, is                    B. was, was               C. is, was                  D. was, is

答案选C，上文说“他”变化很大，即“他”现在不是过去的那个样子了，故第一空填is，第二空填 was（其实第二空也可用 used to be）。请看类例：(from www.nmet168.com)

“Look! That may be the same tree that we happened to see two hours ago.” “My God. We _________ back where we _________.

A. are, are                B. were, were              C. are, were             D. were, are

答案选C，We are back where we were 的意思是“我们现在又回到刚才来过的地方”。