The answer is electrons.
A covalent bond is a type of chemical bond where atoms share electrons. Covalent bonds are also referred to as molecular bonds because they form molecules when bonded.
This type of bond occurs between non-metals. An example of a compound or a molecule that is formed through covalent bonding is water. It is a combination of two hydrogen atoms bonded with an oxygen atom. H₂O
White blood cells that produce antibodies - Lymphocytes
Systems of blood vessels that are responsible for removal of bacteria from the blood stream - lymphatic system
Outer layer of the skin - epidermis
Inner layer of the skin - dermis
The correct answer for your question would be, C
I think the answer to this problem is a) the failure to make your decisions about your body can lead to lowered self-esteem