以下題目是要選出文法錯誤的地方:
1
The reason I will not be going to Mexico this year is because
(A) (B) (C)
I will use up all my travel money attending an important meeting
(D)
in Singapore.
答案是C，為什麼呢？
2
If you knew how many pieces Mary ate for breakfast this morning,
(A) (B)
you would never have doubted why she is overweight.
(C) (D)
答案是A，為什麼呢？
3
For decades, researchers have studied the effects of young blood on
(A)
ageing in mice through a technique called parabiosis, which an old
(B) (C)
mouse is sewn together with a younger one so that they share a
(D)
circulatory system.
答案是C，為什麼呢？
拜託大家幫忙解惑，謝謝！

https://brians.wsu.edu/2016/05/25/reason-because/The reason不和is because合用，因為"because"意思重複。不過美國日常上還是常有人這樣子講，也因此這網站(也有出同名書)列的"common errors"是針對美國人寫的2. 答案給錯。(C)doubted -> doubt3. which 在關係子句裡頭的角色是什麼？它是誰的主詞？是誰的受詞/補語？

謝謝d大! 第2題我少打了一個have。這樣的話，A為何錯呢？

https://tinyurl.com/y9kfdfde 你的題目出自這篇

謝謝d大的連結!

2 不是只能用subjunctive（意思不同而已）。你更正題目後就只能用 subjunctive(A) knew -> had known 因為是針對後頭的"you wouldnever have doubted..."(過去 (事...相反))是因為整體文意/整體意思是否合理的關係，倒不是因為前頭if-claus不能用和現在事實相反的subjunctive(context合適的話自然能用)

了解! 感謝d大解釋!!