Alpine ecosystems are typically dominated by grass and low growing shrubs with an average temperature of 40 and 60 degrees F. Tundra ecosystems on the other hand are extremely harsh, cold and unforgiving environments with a typical temperature of around 37 degrees F.<span />
I believe the answer is: A. De-escalation
At that time, the united states troops was losing on the battle of vietnam. The majority of united states citizens who originally supported the war started to voice up their concern and demanded the government to end the war. So Nixon created de-escalation policy to gradually pull united states troops from Vietnam.