周期麻醉药的作用机制是（）
A.阻断Na+通道
B.促进K+通道
C.抗胆碱作用
D.阻断Ca2+通道
E.抗肾上腺素作用
参考答案：A
He was really disappointed to find that he had failed to make himself ______, although he tried his best to describe vividly.
A．pay attention
B．paying attention to
C．paid attention
D．paid attention to
自外周血进入组织发育为巨噬细胞的是
A．粒细胞B．淋巴细胞C．浆细胞D．巨核细胞E．单核细胞
