人体内产生自然对比最明显的部位是()
A.胸部
B.腹部
C.躯干
D.四肢
E.头部
参考答案:A
.
As I grew up in a small town at the foot of a mountain, the visit to the village_____ scenes of my childhood.
A.came up
B.called up
C.took up
D.made up
CO2气体保护焊时,产生氮气孔的原因有()
A.CO2气体流量过小
B.喷嘴距焊件距离过大
C.焊件表面有铁锈
D.焊件表面有油污