---What useful book !---Yes, it is. But I find it difficult for me to read.A. an, veryB.

---What useful book !
---Yes, it is. But I find it difficult for me to read.
A. an, very
B. a, too
C. an, too
D. a, quite

A. an, very(答案→)B. a, tooC. an, tooD. a, quite解析：本题的上半句为感叹句，修饰名词book用what，名词为可数名词单数，需加不定冠词，useful第一个音为辅音音素，要用a，故不选AC，本题回答语的含义是我发现那本书太难了而看不了，too……to表示太……而不能……的意思，故本题选B。

这个解释是对的