婴儿（4周~1岁）口腔保健的内容是（）
A.睡前吃些零食
B.教会孩子刷牙
C.擦洗萌出的乳牙
D.增加睡眠时间
E.定期免疫注射
参考答案：C
When something is on fire. People throw sand (沙子) on it to put out the fire. The main use of the sand is to
________. [ ]
A. protect the thing on fire.
B. add weight to the thing on fire.
C. keep the air away from the thing on fire.
D. lower the temperature of the thing on fire.
人工边坡
