皮带输送机的主要作用就是靠它的皮带将工件输送到下一工序,通过()或速比控调节到所需速度进行工作的。
参考答案:变频器
Since she is out of work, Lucy________ going back to school, but she hasn’t decided yet.
A.had considered
B.has been considering
C.considered
D.is going to consider
设矩阵A=(aij)4×4,B=(bij)4×4,且aij=-2bij,则行列式|B|=
A.2-4|A|.
B.24|A|.
C.-2-4|A|.
D.-24|A|.