David _____ likes Beijing Opera.[ ]
A. also
B. too
C. either
D. doesn't
答案：A
在图中作出人看到球的光路图．
风心病二尖瓣狭窄伴房颤最易出现
A．呼吸道感染B．心力衰竭C．心律不齐D．亚急性感染性心内膜炎E．栓塞
