b) to mountain-bike
since the sentence follows along with to run and to swim the answer has to be "to mountain-bike".
Answer and Explanation:
As Nelly narrated her story and described events that occurred in the lives of certain characters/people during the previous winter, Lockwood, a stranger, was being entertained up to a point that Nelly wondered how long Lockwood would remain a stranger without falling in love with one of the characters: Catherine. Thus, Nelly hoped that Lockwood would fall in love with Catherine, and marry her. However, although Lockwood saw the possibility of falling in love, he doubted that his love would ever be reciprocated because he was not from the same hometown or land as Catherine.
The answer is B. Hyperbole is just an exaggeration. She doesn't actually think she is going to die from falling down.