单项选择题
A.20 B.30 C.35 D.40
A.1 B.2 C.3 D.4
A.1/3 B.2/3 C.1/2 D.1
A.5--10 B.10--15 C.10--20 D.15--30
A.1;0.1% B.2;0.1% C.2;0.2% D.2;0.3%
A.6 B.8 C.10 D.13
A.1;2 B.2;1 C.1;3 D.2;3
A.50~60 B.40~50 C.30~40 D.20~30
A.5 B.10 C.15 D.20
A.1 B.1.5 C.2 D.3