目前常用的四种气环断面形状分别为（）形、（）形、（）形、（）形。
参考答案：矩；锥；梯；凸圆弧
Look! How excited he is! It is the first time that he _____ so excited since he _____ here last year.[ ]
A. has been; has moved
B. was; moved
C. has been; moved
D. was; has moved
下列哪项属于人工被动免疫( )
A．给机体注射肿瘤疫苗 B．给机体注射百白破C．给机体注射人丙种球蛋白 D．给机体注射LAK细胞
