C
Given that the World population changed little between this time, we can gather than the birth and death rates were similar, since they seem to cancel each other out from 1200-1400. To clarify, think of this. If you add something to a total (think births to population), but take away the same number (think deaths from population) you end up with the same total as before. Because of this, A is the correct answer choice (The birth rate and death rate were about equal).
The correct answer is - biosphere conditions.
The ecosystems and the structure of the vegetation are parts of the wider term that is the biosphere. According to that, any changes that will appear in the functioning of the ecosystems, or if the structure of the vegetation is affected by something, it means that the biosphere is experiencing changes, thus it is becoming affected by this changes.
