請問I wished that ____. 答案(C)he had been happy last year.為什麼不能選(D)he would have been happy last year.?不是也是過去完成式嗎?

wish的四種狀況：
1. a present wish（現在雖抱此希望，但覺得現在不可能實現）
to regret about the present or to talk about things that are unlikely to change
I wish I "had" a job.假設語氣had（名詞子句的動詞用「過去簡單式」，表示現況並不是如此，是現在無法實現的願望）
I wish I "knew" what to do.

2. a present or future wish
to express a desire for a present event or situation to change, or to express impatience or annoyance with another person
I wish Mark "would train" his dog.（would是will的過去式，讓主要動詞train還原成root verb，所以動詞時態雖然還是「過去式」，但不同於「過去簡單式」，是希望「現在」或「將來」可以如此，但希望不大。屬「過去的未來」，時序在過去簡單式之後）

3. a past regret
to express regrets about the past, or to talk about past events or situations that can't change
I wish I "hadn't gotten" this dog.（用過去完成式，表示現在對「過去」事件的懊悔）
We wish we "hadn't bought" this house.
She wishes she "had gone" to college.（過去未能如願，現在感到難過）

4. a past wish
John wished he "had gone" biking instead of hiking.主要動詞wish用過去簡單式，表示這是「以前」的願望。
名詞子句用假設語氣「過去完成式」是因為屬「過去無法實現」的願望。請比較上面第一項的時態（名詞子句動詞用過去簡單式，是現在無法實現的願望）。

你問的狀況屬第四種：
I "wished" that he "had been" happy last year.「過去」無法實現的願望
主要動詞與附屬子句動詞應是「同時」（都是去年的狀況）
如果加上would（表示過去的未來），就會產生「時差」，比「過去簡單式」的主要動詞「晚」。不同時是不符邏輯的，所以錯誤。
請參見上面第二項名詞子句裡的動詞狀況。

would------>had seen
eg:-Would that I had seen him happy last year.
wished-------->had been;
eg:-I wished that (C) he had been happy last year.
eg::-past tense------>past perfect.

If used instead of will with a past tense verb to show what is likely or possible in passive voice:-
=would have been.