The growing speed of a plant is influenced by a number of factors, ________ are beyond our control.

A．most of them

B．most of which

C．most of what

D．most of that

某奶牛，1月前曾发生急性乳腺炎，经治疗已无临床症状，乳汁也无肉眼可见变化，但产奶量一直未恢复，奶汁检测结果体细胞计数55万个／ml。对该牛的诊断是（）。

A.已恢复正常

B.有乳腺增生

C.有乳腺肿瘤

D.有慢性乳腺炎

E.有急性乳腺炎