What are two reasons why the soviets were able to defeat the german army as they advanced on moscow? the germans ran out of men and supplies. russians practiced a scorched-earth policy. spring rains caused tanks to bog down. the winter months proved harsh on soldiers.

I would also like to add:
The Germans had the first offensive and had pushed very close to Moscow, but when they approached Stalingrad, the Germans fell for 3 reasons
1) Like the other answer said, the cold winters which destroyed the Nazi morale
2) The Germans had out run their supply lines and were poorly equipped for another for another offensive. They had little support, low on ammo and food, and did not have winter clothes.
3) Finally the Russians were told that they could not let the city fall because it was of Stalin's namesake.

I would say:
1] Russians practiced a scorched-earth policy.
2] The winter months proved harsh on soldiers.