气体喷射器的喷嘴截面是（）。
A．收缩形
B．扩张形
C．缩放形
D．三种都有
参考答案：B
下列哪项不是哺乳动物的主要特征： [ ]
A．牙齿有分化
B．胎生、哺乳
C．体温不恒定
D．体表被毛
Though in his seventies,the old man is still as ________ as a young man and hates sitting around doing
nothing all day.[ ]
A. enthusiastic
B. energetic
C. talkative
D. sensitive
