一定温度下,向 a L密闭容器中加入1 mol X 气体和2 mol Y 气体,发生如下反应: X(g) + 2Y(g) 3Z(g) ,此反应达到平衡的标志是
They use computers to keep the traffic _______ smoothly.
If you leave the club, you will not be_____back in .
What I need is_____ book that contains ______ABC of oil painting.
Jenny nearly missed the flight______ doing too much shopping.
The CDs are on sale! Buy one and you get ______ completely free.