Final answer:
A 'fortuitous' encounter signifies an unexpected but lucky and advantageous situation, which in Ellen's case, helped her to get her car started. The correct answer is 1.
Step-by-step explanation:
When Ellen had given up hope her car would start, a fortuitous encounter with a neighbor got her back on the road.
The word 'fortuitous' means happening by accident or chance rather than by design, often in a way that is lucky or convenient. In the context of the sentence, it suggests that Ellen's meeting with her neighbor was unexpected and serendipitous, leading to a positive outcome where her car issue was resolved. Hence the correct option is 1.