SL-2B缓蚀剂属于有机吸附膜型缓蚀剂,有效成分()。
A.20%
B.30%
C.40%
D.50%
参考答案:B
The large grassland, reaching out far away, looks extremely beautiful _______ the blue and clean sky.
A.with
B.against
C.through
D.beyond
气瓶气体不能用尽,必须留有余压,可燃气体和助燃气体的余压为()Mpa。
A、0.2
B、0.3
C、0.49
D、0.6