Explanation:

- By and by is an idiom that typically means eventually or after a while, indicating a gradual process or unfolding over time.

- Option 1: Suddenly

This means quickly or unexpectedly. It is not a gradual or eventual process.

- Option 2: By any means

This suggests doing whatever is necessary to achieve something.

- Option 3: Gradually

This reflects the correct meaning of "by and by," indicating something happening slowly or over a period of time.

- Option 4: On the whole

This phrase means generally or considering everything.

.