The correct answer is - C. The birthrate is higher than the death rate.
In general, the circumstance that allows a positive population growth, is when the birthrate is higher than the death rate. In essence, this means, that the number of children born should be higher than the number of people that are dying, in a particular time frame, usually one year.
Still, it is worth noticing, that something like this can fool us on the short term, as a nation can have higher birthrates than death rates, but relatively low birthrates. The life expectancy in the nation can be pretty high, so for a certain period of time the population will still grow, but on the long term, it will experience a sudden decline.