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