英文文法identity 跟 identification

1.
identity 跟 identification 有什麼不一樣?
我看到 identity crisis ,為什麼不能用 identification crisis?

2.
The man, _______, is going to give a lecture at our school.
為什麼答案是 whom I came across yesterday
不能是 that I saw yesterday? 呢
差別在哪裡呢?
2 answers 2