Explanation:

- "The river overflew it’s banks in the monsoon." contains errors.

- "Overflew" is incorrect since the past tense of "overflow" is "overflowed."

- "It’s" is wrong as it should be "its," which shows possession.

Option 1: overflew its bank

- "Overflew" is not the correct past form of "overflow."

Option 2: overflows it’s banks

- "Overflows" is a present tense verb.

- "It’s" is incorrect here.

Option 3: No substitution

- The original sentence is incorrect.

Option 4: overflowed its banks

- Uses the correct past tense "overflowed."

- Uses "its" correctly to show possession.