During the carboniferous period, plants and animals grew very large due to high concentration of a. oxygen in the atmosphere. b. nitrogen in the atmosphere. c. carbon dioxide in the oceans. d. argon in the oceans .

Option A, oxygen in the atmosphere

Explanation:

The highest level of oxygen reached during this phase of the geological cycle of earth. The oxygen level in  Carboniferous  period accounted for 35%  as compared to 21% of oxygen in the atmosphere in present time.

Due to high oxygen content, the giant and wide varieties of terrestrial animal and plant species evolved. For example – size of insects and carwlies increased, plant became extremely giant, increase in number of tree ferns etc.

more words for this could be abiotic and biotic

abiotic: living organisms within an ecosystem

biotic: non-living organisms within an ecosystem

the correct answer is - d. china has a large and growing population.

the fact that china has a large (the biggest) population, and it is still growing, doesn't hinder the agriculture production in the country. in fact, it can for increased production in the agriculture, since there's more labor force, as well the sheer mass of people produces lots of scientists that come up with new inventions as to how to improve this sector. nice example is the inner mongolia region in china, in general dominated by the gobi desert, but few scientist came up with a nice idea as to how to make the region productive by using plants that are very resistant to droughts, so lots of people have been employed, and the region is becoming greener and greener each year, and the production of food in this region is also increasing.