These are our books , ? [ ]
A. aren't these
B. are these
C. aren't they.
D. are they
答案:C
静脉注射碘过敏试验,注药后观察反应的常规时间是()
A.5分钟
B.15分钟
C.25分钟
D.35分钟
E.45分钟
植物根系分哪两大类?