单项选择题
A.20% B.30% C.40% D.50%
A.14~21 B.10~14 C.7~10 D.3~7
A.1/2 B.1/3 C.1/4 D.1/5
A.15%~20%B.20%~25%C.25%~30%D.30%~35%
A.50cm B.55cm C.60cm D.65cm
A.3/4 B.3/5 C.1/2 D.2/5