圆筒型轴承的顶部间隙是椭圆型轴承的()。
A、2倍;
B、1.5倍;
C、1倍;
D、1/2倍。
参考答案:A
Through years of hard work, Mrs. Smith, who ____ as a secretary for five years, is general manager of the company now.
A.serves
B.served
C.has served
D.had served
下列属于通过热传递改变物体内能的实例是( )
A.人类最早的取火方式--“钻木取火”
B.电热毯中的电阻丝通电后温度升高
C.冬天,用热水袋取暖
D.巨大的陨石堕入大气层后变成流星