高粘携砂液的粘度为（）。
A、50～100mPa•s
B、300～400mPa•s
C、500～700mPa•s
D、800～900mPa•s
参考答案：C
电阻R1、R2串联在电路中已知R1：R2=3：2则通过的电流之比I1：I2=______，电阻两端的电压之比U1：U2=______．
.If we humans beings continue to waste and destroy natural resources without using _____ energy, such as the energy from the sun, wind and water, our earth will be done for.
A．alternative
B．solar
C．conventional
D．recycled
