Which is a characteristic of the part of the atom marked "A"?

It contains most of the mass.
It is negatively charged
It is mostly empty space.
It is composed of electrons.

Before the can be observed by using a transmission electron microscope, cells are sliced into very thin sections. what disadvantage does this procedure present in the study of cellular parts

What is a traditional chinese touch therapy involving finger pressure applied to specific areas of the body to restore the flow of qi.

Aperson with age is more likely to catch diseases that healthy people usually don’t catch. what are these infections called?