How did rivers affect the interaction between prehistoric groups?

a. they protected groups from invasion.
b. they invited interaction with other regions.
c. they kept groups separate most of the time.
d. they let groups divide and form unique cultures.

Where did the term “iron curtain” originate? the warsaw pact used the term iron curtain as a code word for communism. in a 1946 speech, british prime minister winston churchill said an iron curtain had fallen across the continent of europe. while visiting western europe in 1946, u.s. president harry truman commented that the mountains there looked like iron curtains. russian general secretary joseph stalin instructed citizens of eastern europe to hang iron curtains over their windows to protect themselves from stray bullets.