[单选题]
1. Carbon is the basis of biological polymers bemr d2)3hekkf sb7q ,4bcg x: q2q(fzd;wause:
I It can form chains by bonding to other carbon atoms.
II It is found in carbohydrates.
III It can form four covalent bonds.
IV It can form branched and ring structures.
A. I only
B. I and II only
C. I, III and IV only
D. I and III only