It was the principles I learned from my reading enabled me to get bigger and better jobs.A

问题补充：

It was the principles I learned from my reading enabled me to get bigger and better jobs.

A. that

B. which

C. what

D. who

答案：

(答案→)A. that

B. which

C. what

D. who

解析：考查强调句：句意：就是我从阅读中学到的原则使我能够得到更大的更好的工作。这是强调句，结构是：It is/was+强调部分+其余部分….,这句话强调的是主语：the principles I learned from my reading，如果把强调句结构去掉这句话仍然成立，就是强调句，选A。