金属凝固后内部化学成分和组织的不均匀现象称为偏析，会影响铸件质量，对（）尤为明显。
A.大型铸件
B.中型铸件
C.小型铸件
D.大型锻件
参考答案：A
-- Not knowing what style of iPad to choose, _______.
A．some advice was given to Liming
B．Liming had to consult his IT teacher
C．so Liming had to consult his IT teacher
D．Liming’s IT teacher gave him some advice
两颗人造地球卫星，都绕地球作圆周运动，它们的质量相等，轨道半径之比r1 /r2=1/2，则它们的速度大小之比v1/v2等于（ ）
A．2
B．
C．1/2
D．4
