英文白痴問題請教.. - 自學

1. 約翰昨天被湯姆看到
John was seen(不是saw吧) by Tom yesterday 這樣對嗎?

2. Architecture is a profession _____ has always interested me.
為什麼答案是which?
(為什麼不能用in which?)

3. The CEO has not decided _____ of the two strategies he should adopt.
為什麼答案是which?
(為什麼不能用what?)

謝謝各位~

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