下列特征中不能判断海马是鱼类的特点是 [ ]
A．有鳍
B．用鳃呼吸
C．终生生活在水中
D．变温
答案：D
The H1N1 flu spread very quickly at the beginning, __________, many people were ill.
A．therefore
B．instead
C．in advance
D．however
为尽量减少心房颤动患者发生体循环栓塞的风险，应首选的药物是（）
A.阿司匹林
B.华法林
C.氯吡格雷
D.低分子肝素
E.普通肝素
