Some little boys have difficulty their hearts into the lesson for a long time.
A. to put
B. to put
C. putting
D. puting
网友回答
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。