有一无色透明溶液，欲确定是否含有下列离子：K⁺、Mg²⁺、Al³⁺、Fe²⁺、Ba²⁺、NO₃^﹣、SO₄^2﹣、Cl^﹣、I^﹣、HCO₃^﹣，取该溶液的实验如下：

            实验步骤

           实验现象

Jim：Hi, Kate！What's the weather like in Shanghai today?

Kate：Hi, Jim！It's sunny and warm here. I'm going to the zoo this afternoon.

Jim：Sounds good.

Kate：Jim, how's the weather in Beijing now?

Jim：It's cloudy. It's going to rain. So I can't fly a kite in the park.

Kate：Oh, I see.

Jim：Do you know the weather in Guangdong?

Kate：It's too hot. The children there usually go swimming in the river.

Jim：Oh, I like swimming, too. But I can't swim now. It's cold here.

一辆汽车以20m/s的速度沿平直公路行驶，当汽车以大小为5m/s²的加速度刹车时，刹车2s内与6秒内的位移之比为（   ）

下列方程是一元二次方程的是（　　）