碳不完全燃烧时的发热量比Si，P的发热量低，但碳元素是转炉炼钢的主要热源。
参考答案：对
— Paper _____ wood. We should not waste paper.
— I agree. I always use _____ sides of paper. [ ]
A. is made of, either
B. is made from, both
C. makes of, both
D. makes from, either
以下哪项不是牙髓的特点（）
A.被坚硬的牙本质壁包围
B.基质富含纤维且具有黏性
C.有丰富的侧支循环
D.牙髓是一种疏松的结缔组织
E.牙髓对刺激只表现为痛觉
