In your study unit, a relationship is compared to a car to point out that

Aany relationship can be "driven" too fast or too slow.
Bpast relationships are like old cars.
Ca new relationship gets more attention than an old one.
Drelationships require regular maintenance.

Verified Answer :

It would be best to have a context for this question, but from what I can see the best answer is the last one:  that relationships require regular maintenance. All the other options are not very helpful advice about how to have a healthy relationship.