Topics: Conditional Sentences

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I did not understand what the lecturer was saying because I had not read hisbook.

A. What the lecturer wrote and said was too difficult for me tounderstand.

B. The lecturer’s book which I had not read was difficult tounderstand.

C. I found it very difficult to understand what the lecturer said in his book.

D. I would have understood what the lecturer was saying if I had read his book.