双联火道带废气循环的焦炉，其特征是每对火道的隔墙下部有废气循环孔，上部有跨越孔。
参考答案：对
下列计算正确的是（ ）
A．3x-2x=1
B．x•x=x2
C．2x+2x=2x2
D．（-a3）2=-a4
Betty's never seen a three-D movies, ?
A．does she
B．isn't she
C．has she
D．hasn't she
