The answer to this should be B.
A) I was cross with this answer and B, because with unemployment it makes things harder for the person to stay in the city because well they are unemployed. But I doubt it could affect everybody around them.
B) the reason it is b is because if there isn't enough farming land for farmers to grow their crops and sell them to the city, people won't live their because without the farming lands the city's economy will be horrible. The food prices will go up which will make things harder for the people to afford especially if they are unemployed. If the city's economy isn't all that good it could affect the population growth rate. That is why this should be the answer.
C) this could be a good answer but I don't think this could affect the population of a city-state.
D) Same with this answer, sure people could move to the suburbs but that doesn't mean they don't have jobs in the city-unless they are unemployed.
So the answer is B.
Hope this helped :)
Have a great day