某男孩为色盲患者，但他的父母、祖父母、外祖父母色觉均正常。该男孩的色盲基因来自于（）
A.外祖父
B.外祖母
C.祖父
D.祖母
参考答案：B
1.___________ (专家) say we should walk at least 10,000 steps one day.
2. In the past, people's jobs_________（需要）more physicaleffort.
3. The wrong diet means you'll put on_______(重量).
4. Watching too much TV has a bad_______(影响)on your study.
复合吹炼强搅拌采用（）作为底吹气体。
A.O2
B.N2
C.CO2
D.Ar
