He found it increasingly difficult to read, ______ his eyesight was beginning to

题型：不详难度：来源：

He found it increasingly difficult to read, ______ his eyesight was beginning to fail.

A．though

B．for

C．but

D．so

答案

B

解析

句意为：他发现阅读逐渐地困难起来，因为他的视力开始慢慢下降。A项意为“尽管”，B项为“因为，由于”，表明附加或推断的理由，引导的分句前常有逗号，for分句一般不放于句首。But表示转折，so表示“因此”。根据句意可以知道，后面一句话是用来解释说明前一句的，所以用B项最佳。