下图是工业区位因素影响力模式图（图中各点与中心距离的长短表示各区位因素影响程度的大小）。读图完成下列问题。

由于国际原煤价格上涨，少数不法商人把一种黑色石头掺在优质煤中高价出售，客户为了不上当受骗，辨别煤中是否掺杂的最恰当方法是检测下面哪一个物理量（）

    My name is Xiaoming. I get up at half past six. I have breakfast at seven o'clock. I go to school at eight o'clock. I have lunch at twelve o'clock. I go home at four o'clock. I have dinner at five o'clock. I watch TV at half past six. I do my homework at seven o'clock. I go to bed at nine o'clock.