C is the only right answer. It is VERY common to see "here here" or "here-here." I think maybe those people who use it that way think they're identifying themselves--right THERE!--as being in agreement. But that's not what this phrase was coined to mean.

"Hear hear" is closer, but it needs the comma because it is actually short for a very old Parliament phrase that used to be "hear him," which got shortened to "hear" and then sometimes got repeated for emphasis. It's also allowed to say "Hear! Hear!" But no matter what, it's something that's being repeated, so it either needs separation with a comma or separation with final punctuation. Incidentally, you might see the hyphenated form if it's referring to "can I get a hear-hear?" or something like that--using it as a noun. But when it's just the phrase itself, it can't just have a space, and it's certainly not going to be using "here."