What Is the Function of Malonyl ACP in the Biosynthesis

What is the function of malonyl ACP in the biosynthesis of fatty acids?

A) to oxidize the β-carbon of the growing fatty acid chain
B) to add two-carbon units to the growing fatty acid chain
C) to shorten the fatty acid chain by two-carbon units
D) to isomerize the trans double bonds in fatty acids to cis double bonds
E) None of these are correct; malonyl ACP is used in β-oxidation of fatty acids.