The correct answer is D. All of these factors.
The polar regions of Earth are characterized by short growing seasons, frozen or snow-covered ground, and low rainfall. These factors make it difficult for trees to grow in these regions.
The growing season is the period of time each year when the weather is warm enough for plants to grow. In the polar regions, the growing season is very short. This is because the sun does not rise above the horizon for several months each year. During this time, the ground is frozen and there is no light for plants to grow.
The ground in the polar regions is often frozen or snow-covered. This makes it difficult for trees to grow roots and absorb water and nutrients. The ground is also very dry in the polar regions. This is because there is very little rainfall in these regions.
The combination of these factors makes it difficult for trees to grow in the polar regions.