What action did stalin take that heightened the tension between the u. s and ussr?

Stalin took a number of actions that heightened the tension between the US and USSR.

Berlin Wall:  He was able to show the power of the USSR, and make a symbol of Communism that stopped people from entering the Democratic nations.

Supplying other Communist countries and rebels:  The USSR helped supply the rebels to take overthrow standing governments and setting up Communist governments. Because the US did not want Communism to spread over the world, it heightened the Cold War tension.

Supplying nukes to Cuba - Cuban Missile Crisis:  The USSR supplied ~100 nuclear weapons to Cuba, which made the weapons close enough to strike the US. The US then took steps to contain the missiles. It ended with the Russian nukes being returned home, and the US missiles were removed from Turkey and other NATO nations near the USSR.

Iron control: Stalin started the hate because he did not give more rights to his citizens, and this heightened the tension, because the US wanted him to give his people more rights. 

hope this helps

Ithink the answer is b : )