An ecosystem is balanced when

a. energy does not enter or leave the ecosystem.

b. there are an equal number of plants and animals.

c. there is plenty of rain.

d. there are enough resources for every living thing.

The answer is "D" because it makes sense everything on earth needs resources to live and if everything during have all the resources needed then the ecosystem would collapse. Example: a lion eats deer if the deer didn't have food to eat then all of its species would die out and then the lion won't have much meat to eat.

D is the correct answer