The correct answer is A. rivalry.
Rivalry is a feeling of competition between two people or groups. It can be friendly or hostile, but it always involves a desire to be better than the other person or group. In the case of the two families, the rivalry is likely due to a history of conflict or disagreement.
Option B, competition, is similar to rivalry in that it involves a desire to be better than someone else. However, competition is not necessarily hostile. It can be a healthy way to motivate oneself to improve.
Option C, friendliness, is the opposite of rivalry. It is a feeling of goodwill and affection towards another person or group. There is no competition or desire to be better in a friendly relationship.
Option D, suspicion, is a feeling of doubt or mistrust. It is often based on negative experiences or information about the other person or group. In the case of the two families, the suspicion may be due to the rivalry between them.
In conclusion, the correct answer is A. rivalry.