If you have a serious infection that cant be effectivly treated in any other way.
you should use a needle
yes
The scientist should use an electron microscope
Yes. I had to use crutches when I sprained my ankle. If you walk on it, it won't heal. And limping is fatiguing.
When the high-powered objective is in position.
Yeah, that is fine.
You should use "are".
You should use did.
you should use meters
You should use your treadmill on a regular basis. You should use it every day if possible. You should use the treadmill for twenty to thirty minutes.
you should use you all
Why should you improve your ability to use the library?
There are number of different kinds of gas you should use. The gas you should use depends on the situation.
You should not. You should use centimetres.
we should use had if the sentence is in past tence
if we made mistake
you should use spagetti and sauce