贮煤场中煤发生自燃的主要原因是（）。
A.煤中挥发份含量太高
B.煤中含碳量的高低
C.空气中氧的作用
参考答案：C
He started to walk faster and the children had to run to ________him.
A．come up with
B．catch up with
C．keep up with
D．put up with
哪些是我国允许使用的抗氧化剂
A．二氧化硫B．糖精C．山梨酸D．亚硝酸钠E．异山梨酸钠
