—Are those your friends?
—Yes, ______.
A. they are
B. they're
C. they aren't
答案:A
补焊后冷却至少()小时,才能进行无损检验。
A.12
B.24
C.36
D.48
下述哪项措施。无助于提高X线照片的清晰度()
A.小焦点投照
B.使用滤线器
C.缩短焦-物距
D.缩短物片距
E.固定投照肢体