---Mr. Wang, I have trouble the test.---Remember it three times at least.to understand; r

---Mr. Wang, I have trouble the test.
---Remember it three times at least.
to understand; reading
B. understanding; Reading
C. understanding; to read
D. to understand; to understand

解析：考查固定结构。have trouble (in) doing sth.在做某事方面有困难；Remember to do sth.记得去做某事；Remember doing sth.记得做过某事。句意：王老师，我在看懂这个测试上有些困难。记住至少看三遍。所以选C。

回答的不错