Explanation:

- Option 1: Not being alert

- Incorrect. This does not match the meaning of the idiom.

- "Be all ears" implies focused attention, not a lack of alertness.

- Option 2: Ready to wait

- Incorrect. This does not reflect the essence of "be all ears."

- Being ready to wait suggests patience, not eagerness to listen.

- Option 3: Eager to listen

- Correct. This perfectly captures the meaning of "be all ears."

- It indicates someone is keen to hear what another has to say.

- Option 4: Be content

- Incorrect. Contentment is unrelated to the idea of listening with intent.

- "Be all ears" focuses on listening, not on a state of satisfaction.