He was so pleased with all _____ we had done for him _____ he wrote us a letter to praise for it. [ ]

A. that, that

B. what, that

C. that, which

D. which, what

春小麦穗（），田间管理的主攻目标是一控为主，控中有促，酌情灌水和看苗追肥。

A、分化处于颖片原基分化期至四分体形成期

B、分化处于颖片原基分化期至小花原基分化期

C、分化处于颖片原基分化期至雌雄蕊原基分化期

D、分化处于颖片原基分化期至药隔形成期