Verb choice before "about": supply the most natural verb to describe speaking on a topic. Sentence: I listened, but I had no idea what he was ____ about. Choose the gerund/participle that collocates with "about" to indicate topic.

Given data

• Sentence: I listened, but I had no idea what he was ____ about.
• We need a verb that naturally pairs with about to indicate topic.

Concept/Approach
The common collocation is talk about (be talking about something). Say usually takes a that-clause or direct speech; tell takes an object (tell me/about), and speak is more formal and typically used as speak about/on but the continuous here most idiomatically reads was talking about.

Option analysis
talking — best fit: was talking about. ✅saying — was saying about is ungrammatical; needs what he was saying or what he was saying about X. ❌telling — would require an indirect object (telling me/us about …). ❌speaking — possible with about, but was speaking about is more formal; in conversational tone, talking about is preferred. ❌

Final Answer
talking