Question

smoke rise and expand.
15 \backup needed!\ dads voice crackled. it was high-pitched and wild, lacking its usual restraint. lieutenant mitchells voice took over, and thats when my heart began to pound. eventually, the static became too thick for any transmissions at all. henry joined me at the window. we barely spoke as the winter sun set.
why does the narrators heart pound when lieutenant mitchell takes over the radio
the narrator realizes that his father is having difficulty staying calm.
the narrator is excited about getting to see such a huge fire.
the narrator does not like the way lieutenant mitchell talks.

Explanation:

The text notes the dad's voice was "high-pitched and wild, lacking its usual restraint" before Lieutenant Mitchell took over the radio. This signals the father is in a crisis and losing composure, which alarms the narrator, making their heart pound. The other options are unsupported: there's no mention of excitement over a fire or dislike of Mitchell's tone.

Answer:

The narrator realizes that his father is having difficulty staying calm.