Which sentence is not a suitable correction for the run-on sentence?

My guitar sounds out of tune I think it needs a new string.

A.
My guitar sounds out of tune. I think it needs a new string.

B.
My guitar sounds out of tune, I think it needs a new string.

C.
My guitar sounds out of tune, and I think it needs a new string.
@Irrati0nal

Question

Which sentence is not a suitable correction for the run-on sentence? 


My guitar sounds out of tune I think it needs a new string.
 
 A.
My guitar sounds out of tune. I think it needs a new string.
 
 B.
My guitar sounds out of tune, I think it needs a new string.
 
 C.
My guitar sounds out of tune, and I think it needs a new string.
@Irrati0nal

irrati0nal · Answer

Keep in mind what we went over in the last two questions. 
With that information, what's your guess?