为何在燃烧调节时要有一定的比例？
参考答案：不按比例调节，就会造成空气过多或过少的弊端，为了使燃料充分燃烧得到理想的燃烧温度，所以一定按比例调节。
Would you please keep silent? The weather report ________ and I want to listen.
A．is broadcasted
B．is being broadcast
C．has been broadcasted
D．had been broadcast
一个具有n（n>0）个顶点的连通无向图至少有（）条边。
A.n+1
B.n
C.n/2
D.n-1
