Acid-Base Question

[henryb]

Hey Guys,
Have been trying to figure this question out. Any help appreciated!

Indicate the ionic species that predominate at pH 8
I: NH4(+) II: NH3 III: H3PO4 IV: H2PO4(-) V: HPO4(2-) VI: PO4(3-)
a) I & IV
b) I & III
c) II & V
d) I & V
e) II & VI

How can you tell just by knowing the pH? I'm confused.
How would you work this out if it said at pH 11?

Thanks