黑色粪便常见于( )。
A．进食少量动物血B．服用铁剂、碳末等药物C．下消化道出血D．便秘E．服用维生素C
参考答案：B
解析：[知识点] 粪便检查
I want to ___________ a bus to Shijiazhuang.[ ]
A. by
B. take
C. taking
— Science is so difficult!
— I think you should keep on _____ hard. [ ]
A. study
B. to study
C. studying
