煤中矿物质的来源为：原生矿物质、次生矿物质和外来矿物质。
参考答案：对
Which of the following words best describes the relationship between park officials and neighboring landowners a. Indifferent. b. Intimate. c. Cooperative. d. Disappointing.
中国人民抗日战争由局部抗战进入全民族抗战的标志是( )
A．“九一八”事变 B．“七七”事变C．华北事变 D．“一二八”事变
