以下题目是要选出文法错误的地方:
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，为什么呢？
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，为什么呢？
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，为什么呢？
拜托大家帮忙解惑，谢谢！

https://brians.wsu.edu/2016/05/25/reason-because/The reason不和is because合用，因为"because"意思重复。不过美国日常上还是常有人这样子讲，也因此这网站(也有出同名书)列的"common errors"是针对美国人写的2. 答案给错。(C)doubted -> doubt3. which 在关系子句里头的角色是什么？它是谁的主词？是谁的受词/补语？

谢谢d大! 第2题我少打了一个have。这样的话，A为何错呢？

https://tinyurl.com/y9kfdfde 你的题目出自这篇

谢谢d大的连结!

2 不是只能用subjunctive（意思不同而已）。你更正题目后就只能用 subjunctive(A) knew -> had known 因为是针对后头的"you wouldnever have doubted..."(过去 (事...相反))是因为整体文意/整体意思是否合理的关系，倒不是因为前头if-claus不能用和现在事实相反的subjunctive(context合适的话自然能用)

了解! 感谢d大解释!!