学校饮水氟化时，饮水氟浓度可以为饮水氟适宜浓度的（）。
A．相同浓度
B．2.5倍
C．4.5倍
D．5.5倍
E．6.5倍
参考答案：C
Have you your new classmates yet? [ ]
A. had friends with
B. made friend with
C. got friend to
D. made friends with
立毛肌收缩可帮助（）
A.大汗腺的分泌
B.小汗液的排出
C.皮脂腺的分泌
D.皮脂的排出
