题目

He found it difficult to read, ________ he had a problem with his eyesight. A . but B . for C . or D . so 答案：B我国现存的第一部完整的农业科学著作是A. 《齐民要术》 B. 《水经注》 C. 《伤寒杂病论》 D. 《缀术》