Explanation:

- Rahul saw a monkey plucking blackberries from the tree and ___________________ them into the river.

- Option 1: "drop"

- "Drop" is incorrect as it is in present tense, doesn't fit with the past action "saw."

- Option 2: "eating"

- "Eating" implies consuming the blackberries, not related to the river, hence contextually incorrect.

- Option 3: "dropping"

- "Dropping" fits well as it describes the action of letting blackberries fall into the river. A continuous action, coherent with "saw."

- Option 4: "asking"

- "Asking" is unrelated to the physical action involving blackberries.

- Option 5: "divides"

- "Divides" suggests separation, irrelevant to the scene described.