It protects the nucleus and
Option B. carboxylic acid
For example
CH3 - COOH, is the acetic acid or etanoic acid.
where - COOH is C bonded with O (trhough doble bond) and with OH (with a single bond)
The control is what you keep the same for each one. For example if you are doing an experiment with plants say you water one with lemon juice, one with milk and one with warm water. The control would be they all have the same amount of sun light and soil. So the growing is equal to keep the experiment fair.
Well you didn't list the following. So
Primary elements would be the sequence of amino acids
Secondary would be interactions between nearby residues, such as beta sheets and alpha helices
Tertiary would be the overall 3-D structure, including disulfide bonds
Quaternary refers to interactions among polypeptide chains
