A:to; ought to
B: /; ought
C:ought; ought
D:/; ought to
在线性回归模型y=bx+a+e中,下列说法正确的是( )
①高炉中焦炭的作用是产生一氧化碳
②高炉中焦炭的作用是供热
③高炉炼铁得到的产品是钢
④高炉炼铁的原料有铁矿石、焦炭、石灰石、空气等.
下列物质中,有一种与其它三种物质不属于同一类别的是( )
Jane has ______ from school for 2 years. When she ______ the happy time, she always misses her teachers and classmates.