In the 1950s and 1960s, historians debated the question of who started the cold war. in the 1990s, it became more interesting to ask when it started. why the change, and what questions might historians today ask?

The United States and the Soviets were already unfriendly during the second world war. It most likely became more interesting to ask when it started because they had a grudge against one another long before the cold war actually began. It became less "who started" and more "how long has this actually been going on"

they both built pyramids.

i think the answer is   b.