Mutation is random because there is really no way of knowing whether a child will inherit it, whereas natural selection is predisposed in either parent.
Answer:
Crossing over during meiosis creates genetic variation.
Explanation:
Some elements mentioned above, such as oxygen are present in organic compunds in many occasions, but from all of the options, the one that is always present is:
A. Carbon
Carbon is found in all organic compunds because of the bonds it can form, being able to form up to 4 covalent bonds.
Hope it helped,
BioTeacher101