-- The math problem is not difficultBut after several tries I have to give up on

问题补充：

-- The math problem is not difficult.

--- But after several tries , I have to give up on it .

A. it’s , working

B. itself , to work

C. itself , working

D. its , to work

答案：

A. it’s , working

B. itself , to work

(答案→)C. itself , working

D. its , to work

解析：根据题干，本句的意思是”这道数学题本身并不难。“第一个空是做the math problem的同位语，故应该用itself，表示本身。Give up doing”放弃做某事“，是固定短语。所以本题选C。