Encyclopedia Britannica is an encyclopedia publisher who sells printed encyclopedias. In the $1990$s$,$ encyclop did electronic encyclopedias have on Encyclopedia Britannica?

Electronic encyclopedias

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

B$.$ served as a new product that fills a consumer need better than printed encyclopedias did.

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

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

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