This is not a very well worded question. What do you mean by why should it be used? I Bunsen burner is used for heating things, usually in a lab setting.
Their should be used to describe something (idea or object) that "belongs to them". These are their books. It was their idea.A frequent error, their should not be used when describing something that belongs to a single person when the gender is unknown. His or her should be used in these situations.By contrast, There is a place. Not here, but there. The books are over there.They're is a contraction for the two words "They are." They're looking for their books over there.
true
The reference point should be stationary, or not moving.
a ruler
it should not be used in any country
A skateboard should be used by pushing hard on the ground.
yes they should be used in class
no they should not
Pickles should not be only used on sandwiches.
it should be used for the care of your screen from harmful uv rays
If a drug has expired, it is in a condition and should not be used.
the, an, a when these articles be used
yes it should be used in all netball games
it should be used when someone is ether sick or has an injury which is bleeding
Signposts should be used as often as possible where necessary.
A torque wrench should not be used on any hitch type.