炼焦炉的发展大体可分四大阶段,即成堆炼焦与窑式、倒焰炉、废热式炼炉及现代蓄热式焦炉。
参考答案:对
— What are you going to do this weekend?
— I’m not sure ______. Maybe I am going swimming.
A.also
B.too
C.ever
D.yet
原始地球表面没有生命,但有相当量的游离氧存在。 [ ]