---I find the more we study, the more difficulty we have ________ out Maths problems.

---Oh, I agree with you. Maths is more and more difficult.

A．worked

B．work

C．works

D．working

周公所建构的思想体系是哪家的最主要的思想来源？（）

A.儒

B.道

C.墨

D.法