B.
Explanation:
to find the midpoint the formula is 

so use the points provided and substitute them in to the formula!! 
- (-4,-7) = (x1, y1) 
- (5,6) = (x2, y2) 
so now it would look like this inside the formula 
and then you'll just solve that !! 

so we know x = 0.5 now, solve for y 

and we now know y = -0.5 
 point form (x,y) and you're all done !! 
and this is why the answer is B. (0.5, -0.5)