The tundra is a cold, ice-covered region on earth. recently there has been an increase in the number of plants growing there. this new plant growth is most likely due to
a) an effort by the local people to plant trees.
b) global warming, resulting in warmer temperatures on earth.
c) more people going to the area for recreation and vacations.
d) animals leaving the tundra for warmer regions with less snow cover.

B) global warming, resulting in warmer temperatures on Earth.

Explanation:

Tundra is the coldest biome of the world. It exhibit very low temperature range and treeless plain with snow precipitation. The global warming is the phenomena which is related with rise in global temperature due to abundance of greenhouse gases into the atmosphere. These gases are released into the atmosphere by burning of fossil fuels, industrial gaseous release and deforestation. These gases traps the heat energy from sunlight making the atmospheric temperature warm. As a result of global warming the ice caps and snow bearing areas of the tundra biome will deplete. The melting of the ice will provide proper unfrozen soil for the growth of plants. Hence, new plants will increase in numbers due to global warming.

b tumor cells have a cell wall instead of a membrane

explanation:

tumor cells different from normal cells because tumor cells have a cell wall instead of a membrane.

more words for this could be abiotic and biotic

abiotic: living organisms within an ecosystem

biotic: non-living organisms within an ecosystem