Many of the creatures in the movie Avatar are not real, but much of ________ happens is still attractive.[ ]

A. which  

B. that

C. what  

D. them

引起该患者感染最主要的原因是

A．白血病细胞浸润

B．联合化疗

C．皮质激素的应用

D．代谢亢进

E．成熟粒细胞减少