Which of the Following Statements About Allostery Is TRUE

Which of the following statements about allostery is TRUE?

A) Allosteric regulators are often products of other chemical reactions in the same biochemical pathway.
B) Allosteric regulation is always used for negative regulation of enzyme activity.
C) Enzymes are the only types of proteins that are subject to allosteric regulation.
D) Binding of allosteric molecules usually locks an enzyme in its current conformation, such that the enzyme cannot adopt a different conformation.