Encyclopedia Britannica is an encyclopedia publisher who sells printed encyclopedias. In the $1990$s$,$ encyclopedias began to be sold electronically. What effect did electronic encyclopedias have on Encyclopedia Britannica?

Electronic encyclopedias

A$.$ resulted in the government introducing occupational licensing laws for educational materials.

B$.$ served as a complement, increasing sales of electronic and printed encyclopedias.

C$.$ served as a superior product to heavy, bulky, and expensive printed encyclopedias.

D$.$ used printed encyclopedias from Encyclopedia Britannica as a key input.

E$.$ prompted Encyclopedia Britannica to form the first cartel for encyclopedias.