Step 1: Understanding Arjuna bark.
The Arjuna tree (*Terminalia arjuna*) belongs to the family Combretaceae. This tree is well known for its medicinal properties, particularly for heart health.
Step 2: Analyzing the options.
(A) Combretaceae: Correct — Arjuna belongs to the Combretaceae family.
(B) Gnetaceae: This is incorrect, as Gnetaceae is a separate plant family.
(C) Rutacea: Rutaceae is the family of citrus fruits, not Arjuna.
(D) Solanacea: Solanaceae is the nightshade family, which is unrelated to Arjuna.
Step 3: Conclusion.
The correct answer is (A) Combretaceae as Arjuna belongs to this family.