Select all that apply language is important to humans because it: a.)separates them from the animals b.)allows them to communicate with every person on earth c.)allows them to work with others d.)allows communication of abstract ideas

A must be incorrect (doesn't sound like a reasonable answer).
B is incorrect: Not everyone speaks every language, thus no one can communicate with every person on earth.
C sounds correct - language allows us to operate along with other people.
D also sounds correct, as it would be difficult to try to communicate ideas to people by staring at them really hard.

Hope this helps.

I believe it's A and C and D. (A doesn't really prove the point that language is important to humans, so you decide if I am right or wrong about that!) 

Hope this helps! 

Kthen, just here for points