椭圆$\frac{x^2}{a^2}+\frac{y^2}{b^2}=1\left(a>b>0\right)$的离心率为$e=\frac{1}{2}$，右焦点为$F\left(c,0\right)$，方程$a{x}^2+bx-c=0$的两个实根分别为$x_1$和$x_2$，则点$P\left(x_1,x_2\right)$（　）

比的后项不能是零．

以下符合文艺复兴时期人文主义内涵的语句是（　　）

某同学在做“用电流表和电压表测定小灯泡功率”的实验中，所用小灯泡的额定电压为2.5V，额定功率小于1W．

①则电源至少应选用____ 节干电池串联，电压表的量程应选用0～3V，电流表的量程应选用____ A．

②如图是测量小灯泡的功率的原理图，若连接电路时灯泡接触不良，而其他部分完好．则除了灯泡不亮之外，还会出现的现象是：Ⅰ．____ ：

Ⅱ．____ ．

③排除故障后，该同学设计、并根据实验现象和数据填写的一份实验记录表格：

根据表格内容，试回答下列问题：

Ⅰ．小灯泡的额定功率是____ ；

Ⅱ．小灯泡正常发光时灯丝电阻的阻值是____ ；（保留一位小数）

Ⅲ．在“实验记录”中如果该同学对实验现象的观察和数据的记录都正确，请你指出他所设计的实验记录表格中的一处错误：____ ；

Ⅳ．滑动变阻器在实验中所起的作用：除了可以改变电路中的电流和灯泡两端的电压之外，还可以起到____ 的作用．

Besides calling 120, here is what you should do when no one is around to help.

If you get lost, you may stay where you can be seen clearly and try your best to have a rest. In a wide open area, make a colorful cross out of rocks to show where you stay.

When you choke at home, make a sudden hit against the back of the chair. If you can't breathe after six tries, call 120. Leave the telephone open until help arrives.

Use your hand or a scarf, or any dry cloth you can find, and push down on the wound until the blood stops running. Don't put the cloth around your leg tightly(过紧), or you may lose your foot.

When a fire breaks out, you must move close to the floor. Cover your mouth and nose with a wet towel, make you wet from head to foot if possible and find a safe place outside.