The Battle of Plassey was a decisive victory of the British East India Company over the Nawab of Bengal and his French allies on 23 June 1757, under the leadership of Robert Clive which was possible due to the defection of Mir Jafar Ali Khan, who was Siraj-ud-Daulah's commander in chief
The answer is A because the significance of gunboat diplomacy is military threats which is a foreign policy used to scare the less powerful nation so that they follow the most powerful nations demands.
