D.With
这题考的是因果关系
关系:有好问题要解决=>他们这周未需要很用功
A.Because of:Because of後面要跟noun,但lots of problems to solve不是noun
B.As:as後面要系一句子,即後面要有S V O(subject verb object) ,但lots of problems to solve系缺少左Subject
C.For :for後面要跟noun/verb ,但lots of problems to solve不是noun/ve