sat 语法题.求具体分析

sat 语法题.求具体分析
(a.Whereas ) their friend Sean, who often behaved (b. as if) he had only one day left to live, Rob and Darrin ( c.rarely) acted without (d. first considering) the consequences.(e.No error)

(A)
(B)
(C)
(D)
(E)

Correct Answer: A
Here's Why:
The error in this sentence occurs at (A), where inappropriate word choice creates a sentence fragment (the sentence has no main verb). To fix this problem, “Unlike” should be used in place of “Whereas.”
Question Type: Identifying Sentence Errors
为什么a错了.应该如何用 whereas