He found it increasingly difficult; _____his eyesight was beginning to fail.
A. though B. for C. but D. so
He found it increasingly difficult; _____his eyesight was beginning to fail.
A. though B. for C. but D. so
B
解析：此题考查状语从句连词的选择。题意为：他发现读书越来越难了，因为他的视力正开始下降。从题意看，前后句应是因果关系。for引导原因状语从句，表示一种补充说明，通常与主句用逗号隔开。用作连词though意为尽管，but意为但是，转折关系，so意为所以，颠倒了因果关系。均可排除。