暖管时，待蒸汽管道充分（）后，再将锅炉的主汽阀全开。
A.冲洗
B.预热
C.膨胀
D.排水
参考答案：B
The man who thought of ________a gas engine with wheels was the inventor of the automobiles.[ ]
A. comparing
B. combining
C. competing
D. connecting
病人采用鼻导管吸氧时，医嘱要求氧浓度达45%，氧流量此时为( )
A．2L/minB．4L/minC．5L/minD．6L/minE．8L/min
