Final answer:
Elinor finds the secrecy strange because Marianne and Willoughby are openly affectionate and transparent in other aspects of their relationship, making any hidden engagement unexpected.
Step-by-step explanation:
Elinor finds the secrecy about an engagement between Marianne and Willoughby to be strange because:
- They are open about everything else.
- They are clearly so fond of each other.
The discussion seems to be drawn from a scenario that indicates recognition of the closeness between two individuals, suggesting that their behavior is such that an engagement would not be surprising. Considering the level of their mutual affection and their openness in other matters, any secrecy about their commitment to each other would indeed seem out of place.