(a) Sense of unity

• Rationale: Unity symbolizes connection and support. While essential, it is not enough on its own for the family’s development. A family can still grow without unity at every moment, but it does help strengthen relationships.

(b) Specific objective
🎯

• Rationale: While having a specific objective provides direction, it is not a fundamental or essential feature for the development of a family. Families grow through relationships, not just by having set goals.

(c) A form of marriage
💍

• Rationale: Marriage is often associated with family structures, but it is not essential for family development. Families can form in other ways, like cohabitation or adoption, where legal bonds aren’t the central factor.

(d) Mutual understanding
💬❤️

• Rationale: Mutual understanding is vital for healthy family development. Effective communication (💬) and emotional connection (❤️) form the backbone of strong family relationships, making this the most essential feature.

Conclusion:
The most essential feature is (d) Mutual understanding 💬❤️, as it creates the foundation for healthy relationships and emotional growth within a family.