炉腹等部位采用（）冷却壁，它的作用是当该部位砖衬被侵蚀掉后，利于渣皮的形成。
参考答案：镶砖
What caused the accident and who was responsible for it ________ a mystery.[ ]
A. has remained
B. are remained
C. remains
D. remain
Although she has a lot of problems, she manages to remain ________. [ ]
A. optimistic
B. cautious
C. concerned
D. anxious
