An officer（军官）is at a bus stop. He wants to see his girlfriend by bus. He wants to tell his girlfriend the time of his bus, and then she can meet him at the stop in her car. He wants to call his girlfriend on a pay phone（付费电话）,but he doesn't have a coin（硬币）for the phone. He wants someone to help him.

    A soldier（士兵）is near the stop. The officer walks to the soldier and asks,“Do you have any coins for the phone?”

    “Let me have a look,” says the soldier. “I'll see if I can help you.”

    “Don't you know how to speak to an officer?” says the officer. “Now let's say it. Do you have any coins for the phone?”

    “No, sir,” says the soldier.

无锡市环保检测中心网站公布的2017年4月某日的PM2.5研究性检测部分数据如表：

则该日这6个时刻的PM2.5的众数和中位数分别是（   ）

①若 $a>1$ ，则 $a^2+a-2>0$ ；②若 $a^2+a-2=0$ ，则 $a=1$ ；

③若 $b^2=ac$ ，则 $a,b,c$ 成等比数列；④若 $a+c=2b$ ，则 $a,b,c$ 成等差数列.

其中真命题的个数为(    )

下列词语划线字注音完全准确的一项是（   ）

小亮用如图装置探究“光的反射规律”：