It's good ______ you to keep ______ when you have something difficult ______. [ ]

A. for; trying; to do

B. of; trying; doing

C. for; to try; to do

D. of; trying; to be done

以下关于爬行类动物脾脏的描述中，最接近哺乳动物脾脏的组织结构是（）

A.表面覆盖被膜，且人实质形成小梁

B.白髓和红髓相间排列

C.弥散性脾索和脾窦

D.椭球周围淋巴鞘或动脉周围淋巴鞘