Answer:
The correct answer is C. The door to the attic creaked open slowly.
Step-by-step explanation:
By definition, mystery is something that is difficult or imposible to explain. Considering that, the only option that creates a sense of mystery is the third option, since the reason for the door opening is unclear or unknown.
For options A and D there is a clear and straightforward explanation.
For option B there is no action in need of an explanation.