电桥按测量线路可分为()。
A.单臂电桥和双臂电桥;
B.精密电桥;
C.专用电桥;
D.小电桥。
参考答案:A
正常二尖瓣开口面积为()。
A.4~6cm2
B.2~4cm2
C.3~4cm2
D.1~2cm2
E.6~8cm2
Unitl tens of years ago, most zoos in such a way—animals in one area and birds in another.
A.were organized
B.had organized
C.will organize
D.have been organized