维生素D进入细胞不需载体,也不需消耗能量,主要原因是[ ]
A.维生素D本身就是载体
B.细胞膜的基本支架是磷脂双分子层
C.细胞膜具有一定的流动性
D.维生素D是小分子
答案:B
As he works in a remote area, he visits his parents only__________. [ ]
A. occasionally
B. anxiously
C. practically
D. urgently
妊娠合并外科疾病,下列哪种不常见()
A.卵巢囊肿
B.上消化道穿孔
C.子宫肌瘤
D.急性阑尾炎
E.急性胆囊炎