The correct answer is B) intense cold of Winter.
What made fighting on Russia soil especially difficult for German troops was the intense cold of Winter.
The Mozhaisk area where the Nazi troops tried to fight against the Russian Army during World War II, the weather was extremely cold reaching the -40 Centigrade degrees.
The other options of the question were, a) intense heat of some, c) lack of access to water, and d) mountainous terrain. German troops had difficulty to move off roads due to the deep snow in the forest. German operations were very limited. The Russian Fifth Army had a great advantage when they used special ski troops. So what made fighting on Russia soil especially difficult for German troops was the intense cold of Winter.
