Select the most appropriate option to complete the sentence.
I listened, but I had no idea what he was ______ about
(A) saying
(B) telling
(C) talking
(D) discussing

Hint: Some words are similar in colloquial language but there is a lot of difference in their grammatical use, such words are called confusing words. Like-
Affect / Effect- Affect is typically a verb: the humming of Chester influenced the ability of poetry to focus. Usually, the effect is a noun: Chester was sorry for the effect that his humming had.

Complete step by step answer:
‘TALKING’ is the speaking action. The speaker was listening, but he had no idea what he was talking about. Thus, the correct answer is Option C.
I listened, but I had no idea what he was TALKING about

So, the correct answer is “Option C”.

Additional Information:
‘Tell’ means "to provide a person with details," so a person always follows tell (present) and told (past). For example - Tell me about the movie. Did you like it?
With ‘say’ (present) or said (past), we can use these structures:
 say (something), say that (something), say (something) to (a person), “(something)” a person said. For example- Francis says she doesn’t like chocolate.
Saying means saying words or sounds, voicing a thought, opinion, or suggestion, or stating a fact or guidance. For example: "Never forget to say’ Thank you’ and’ Please.’
Speaking involves simply saying things out loud; speaking to someone. For example: "I'm really glad my dogs can't talk."
The distinction between talking and talking as verbs is that talking is when talking is. The action of the verb talk is talking as a noun.

Note:
We should be careful while using confusing words as there is only a slight difference in their use and this difference can become the reason for our answer being wrong.