The correct answers are they are open about everything else and they are clearly so fond of each other.
Throughout the story it is shown that these characters share a passionate almost childish love, there are no preconceived concepts between them and they both act in their purest versions apparently , until a turn of events that showed reality.
Options 1 and 4 are not correct because Marianne's family was not the richest so the possibility of having plenty of money is not possible, They didn't know about the engagement until later in the story.