Final answer:
The correct answer is C. -[infinity] since an unbounded decreasing sequence tends to negative infinity as it does not have a finite lower limit.
Step-by-step explanation:
If (sn) is an unbounded decreasing sequence, the behavior of the sequence as n becomes very large is of interest. A sequence is said to be unbounded if it does not approach a finite limit. In this case, if the sequence is decreasing and unbounded, it means that the numbers in the sequence continue to decrease without bound as n approaches infinity. Therefore, the correct answer is C. -[infinity] (negative infinity), because as the sequence continues to decrease without bound, it gets closer and closer to negative infinity.