He found it increasingly difficult to read, his eyesight was beginning to fail.
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He found it increasingly difficult to read, _____ his eyesight was beginning to fail.
A. and B. for C. but D. or
试题答案
B
because语势最强,用来说明人所未知的原因,回答why提出的问题; since是双方都知晓原因或经过分析而得之的原因, ;for是并列连词,前用逗号隔开,表逻辑推理或补充说明;as语气最弱,原因是显而易见的或已为人们所知。