A:dangerou
B:a danger
C:in danger
D:dangerous one
某同学利用如图装置测定空气中氧气的含量,红磷燃烧后恢复到室温,打开弹簧夹发现进入广口瓶中的水的高度不足广口瓶容积的15.造成这一现象的原因不可能是( )
- Has David finished his project yet?
- I guess not. He ___________ on it at lunch time. Do you want me to confirm it?
小丽患了佝偻病,她吃钙片的同时,应该让她服用( )