Mr. Smith is busy these days a new book on how to develop a child’s reading skill.A. work

问题补充：

Mr. Smith is busy these days a new book on how to develop a child’s reading skill.

A. working out

B. working on

C. working for

D. working with

答案：

A. working out

(答案→)B. working on

C. working for

D. working with

解析：本题的含义是史密斯先生这些天正忙于写一本有关培养儿童阅读技能的书，work on表示忙于或从事的意思，符合本题含义，故本题选B。