Please help 15 pts!!

Which element provides strength to the exoskeleton of clams and oysters

What do all macromolecules have in common with each other? oa. they all are formed from the same elements.ob. they all have major roles in cell membranesoc. they all act as catalysts in the body.od. they all have peptide bonds between carbon atoms.

Acceleration is a direct result of a.) balanced forces b.) unbalanced forces c.) gravity d.) velocity