加热炉点火时一次点不着，炉膛应吹入（），再按点火步骤点火。
A.蒸汽
B.空气
C.氮气
D.瓦斯
参考答案：A
Not until his father died ____ what his father really meant. [ ]
A. do they realize
B. did they realize
C. realized they
D. had they realized
勾芡的基本方法有摇推和翻伴两种，其中摇推的作用是（）
A.使菜肴汤汁浓稠，汤菜相融
B.使芡粉汁全部裹在原料
C.使芡粉与原料分离
D.是菜肴汤汁稀松
