Number four is confusing me if you know halp

the answer is d (apex) good luck : ))

try using substitution:

x + y - 6 = x - y. (i'm not giving you the exact answer). since 0 = x - y, then sub 0 in the equation with x - y. combine your like terms, and then use inverse operations, and you'll have your answer.

: -)

any abiotic or biotic factor in an ecosystem that causes a population's size to slow or decrease is a limiting factor.