Answer:
C
Explanation:
The common ratio can be < 0
All that means is the entry's signs alternate.
For example
r = - 2
a = 3
Series = 3 -6 18 -54 etc. The members of the series become larger and larger in magnitude and the series diverges. It is not clear where it might stop.
-1 < r < 0 gives a much better behaved result.
The point is that c is incorrect.