Following statements were made with respect to symbiotic association of rhizobia with legumes:

A. nodD is a regulatory gene.

B. Nod factors are lipochitin oligosaccharides.

C. Nod factors predominantly have α→1→4 linked N-acetyl-D-gluco- samine backbone.

D. Receptors for Nod factors are protein kinases with extracellular sugar-binding Lys M domain.

Which one of the following combinations represents all correct statements?