冲压无缝弯头是用优质碳素钢、不锈耐酸钢和低合金钢无缝钢管,在特制的模具内压制成型的,其种类有()。
A.45°
B.90°
C.120°
D.U形
参考答案:A, B
— How does Jack usually go to school?
— He _____ ride a bike, but now he ______ there to lose weight.
A.used to; is used to walk
B.was used to; is used to walking
C.was used to; is used to walk
D.used to; is used to walking
我国三国时代著名数学家刘徽是第一个用割圆术找到计算圆周率方法的人,他求出π的近似值为3.1416,如果取3.142,是精确到( )位,有( )个有效数字