Question 18.

" In the late 1960s, purists were suspicious of folk songs recast in rock idioms." Purists oppose any altercation or adaptation of original folk from and they criticized the adaptations by rock too. Hence, option B can be inferred

Folk music was inspired by revolutionary intentions in 1940s, various philosophies and school of thoughts in 1960s, Freedom of expression(Bob dylan) and psychedalia.

This shows a constant transformation of folk reinforcing the beliefs of Cecil Sharp. Option C is correct. Option D can be rightly inferred from the lyrical freedom of bob dylan and revolutionary intentions in 1940s. 

Option A : "In the late 1960s, purists were suspicious of folk songs recast in rock idioms. Electrification, however, comes in many forms." Even though the electrification of folk by rock was rejected by purists, electrification came in many forms and not individually by Rock alone. Hence, electrification of folk music is not causated by rock alone. Hence option A cannot be inferred.