下消化道出血最常见的原因是（）
A.大肠癌
B.大肠息肉
C.溃疡性结肠炎
D.克罗恩病
E.肠结核
参考答案：A
As new driver．I have to practice _______the car in my small garage again and again．
A．parking
B．to park
C．parked
D．Dark
铁水中碳含量一般在（）左右。
A.2.6%
B.3%
C.4%
