泪膜的生理作用是()
A.润滑眼球表面
B.防止角结膜干燥
C.保持角膜光学特性
D.杀死病原菌
E.抵御眼球表面异物和微生物
参考答案:A, B, C, E
Many new workers ________ and after six months they will be sent to build a new railway.[ ]
A. are being trained
B. are training
C. will train
D. will be trained
三七树脂道存在的主要部位是( )
A.木质部B.韧皮部C.栓内层与韧皮部D.韧皮部与木质部E.髓部