Some little boys have difficulty their hearts into the lesson for a long time.A. to putB.

问题补充：

Some little boys have difficulty their hearts into the lesson for a long time.

A. to put

B. to put

C. putting

D. puting

答案：

A. to put

B. to put

(答案→)C. putting

D. puting

解析：

此题考查固定句型结构have difficulty in doing sth表示做某事有困难，其中in可以省略。动词put的现在分词形式putting。故选C。