【单选题】在梯度液中不同沉降速度的粒子处于不同的密度梯度层内形成几条分开的样品区带,达到彼此分离的目的,这种方法是
【单选题】What kind of planet might NOT support life?
A.
Most of the planets of the stars.
B.
Stars similar to our sun.
C.
Planets similar to the earth.
D.
Planets with proper conditions.
【单选题】限制部分自由度就能满足工件加工要求,这种定位称为( )。
【单选题】限制部分自由度就能满足工件加工要求,这种定位称为( )。
【判断题】若圆柱体的底面为水平面,则圆柱体的三面投影是一个圆和两个大小相等的矩形。
【单选题】有一家制造企业,当产量Q=1000时,平均可变成本为6,且平均总成本为10。请问这家企业的总不变成本是多少?
【单选题】---Where is your grandpa? ---He _________ Canada and __________ Toronto for a month.
A.
has been to, has been in
B.
has gone to, has been in
C.
has been in, has been to
D.
has gone to, has been to
【单选题】________ is your birthday? April 8th. [ ]