How did the development of irrigation systems improve living conditions?

A.
It allowed people to move out of town onto farms.

B.
It made people less dependent on trade.

C.
It gave people a surplus of food.

D.
It made people switch from hunting to herding.

Question

How did the development of irrigation systems improve living conditions?
 
 A.
It allowed people to move out of town onto farms.
 
 B.
It made people less dependent on trade.
 
 C.
It gave people a surplus of food.
 
 D.
It made people switch from hunting to herding.

anonymous · Answer

Um. I'm pretty sure the answer is 'none of the above' but it certainly isn't A or D. 
It did improve food production, which directly gives a surplus, and indirectly makes people less dependent on trade. If you can select multiple answers, go with both B and C, if not, C is a more direct consequence.