She was so mad at her boyfriend, she _____ on him when he called.

The choice of "Hung up" is correct because it accurately describes the action of ending a phone call, which aligns perfectly with the context of being mad at someone and reacting by disconnecting the call. This phrase is commonly used to convey immediate emotional responses in conversations, particularly in situations involving anger or frustration.

The grammatical structure used also supports this choice; "hung up" is the past tense of "hang up" and correctly matches the past tense context indicated by "was" in the sentence.

This past action reflects the woman's emotional state at the time of the call, further emphasizing her anger. It captures both the action and the emotional reaction in a concise way, making it the most appropriate fit for the sentence.