1. I still could not understand him.

2. I still don't understand.
3. He was still waiting for her .
4. He has still been looking for the kid.
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Is the position of 'still' correct? Are they all acceptable in terms of grammar?

Yes, all are fine.

yes

Yes, the position of "still" in all four sentences is correct, and they are all acceptable in terms of grammar.

In these sentences, "still" is used as an adverb and is placed before the main verb to indicate that the action or state is ongoing or continuing. Here's how you can analyze the placement of "still" in each sentence:

1. "I still could not understand him."
- "Still" is placed before the main verb "could not understand" to convey that even at the present time, the speaker is unable to comprehend what the person is saying.

2. "I still don't understand."
- Here, "still" comes before the main verb "don't understand" to indicate that the lack of understanding is persistent and hasn't changed up until the present moment.

3. "He was still waiting for her."
- In this sentence, "still" is placed before the main verb "waiting" in the past continuous tense. It means the person was waiting at a particular point in the past and continues to wait at that time.

4. "He has still been looking for the kid."
- "Still" precedes the auxiliary verb "has been" and the main verb "looking" in the present perfect continuous tense. It suggests that the person has been searching for the child persistently up until now.