— ________ my baseball? — It’s under the chair. A. Where B. Where’s C. What’s D. Where are 答案:B
实验室制取氧气大致的几个步骤为:
a.点燃酒精灯;
b.检查装置的气密性;
c.将高锰酸钾装入大试管,用带导管的单孔塞塞紧管口,并把它固定在铁架台上;
d.用排水法收集氧气;
e.将集气瓶装满水;
f.熄灭酒精灯;
g.将导管移出水面.正确的操作顺序是
[ ]
A.
bceadfg
B.
cbeadfg
C.
bceadgf
D.
bcaedgf