What is a possible letter name of the note marked with an "x"?

Buddy Holly was one of the first rock and roll performers to

a. become a commodity. b. gyrate suggestively during a performance. c. record cover versions of songs by other writers. d. write his own songs.

Penderecki's Threnody is based on ideas from ____ of the 1950s

A) aleatoric music B) total serialism C) electronic music D) all of these choices