"singular" or "plural"? - When I want to talk about something general...
When I want to talk about something general like below, which one should I use? I'm not talking about a specific thing with the listner, just taking generally. If any of them are wrong, please correct.

Elephants have a long nose(trunk)
An elephant have a long nose(trunk)
Elepahnts have long noses(trunks)
Elephant has a long nose(trunk)

Birds have a beak.
A bird have a beak.
Birds have beaks.
Bird have a beak.

Question

"singular" or "plural"? - When I want to talk about something general...
When I want to talk about something general like below, which one should I use?  I'm not talking about a specific thing with the listner, just taking generally.  If any of them are wrong, please correct.

Elephants have a long nose(trunk)
An elephant have a long nose(trunk)
Elepahnts have long noses(trunks)
Elephant has a long nose(trunk)

Birds have a beak.
A bird have a beak.
Birds have beaks.
Bird have a beak.

Answer

Elephants have long noses(trunks).
Birds have beaks. 
This is the most common way of describing general qualities. If you start with a plural, you must use plurals for everything else (except uncountables of course).

The other way to say it, but less common, is to use singulars:
An elephant has a long trunk.
A bird has a beak.

Answer

You should use plural all the way through.

Elephants have long noses. Cats have sharp claws. People have faces.

Do you see what I mean?

Answer

Elephants have a long nose(trunk)  (correct)
An elephant have a long nose(trunk) (An elephant has a long nose.)
Elepahnts have long noses(trunks) (correct)
Elephant has a long nose(trunk) (An elephant has a long nose.)

Birds have a beak. (correct)
A bird have a beak. (A bird has a beak.)
Birds have beaks. (correct)
Bird have a beak. (Birds have a beak.)

I hope this helps! :)

Answer

Thank you.  When I talk about things in general, which one should I use, plural or singular?

Elephants have a long nose. --->  My understanding to hear this sentense is that every elephant has a long nose.

Elepahnts have long noses. --->  My understanding to hear this sentense is that elephants have a long nose, but some may have more than one nose.  

I'm a bit confused using singular and plural when taking about general things.