Why did the British Royal Navy attack French warships at Mers-el-Kebir?

a. The French crews had sworn allegiance to Germany

b. France was at war with Britain

c. The French crews refused to surrender their ships when the British requested

d. They were manned by Germans

C. the french crews refused to surrender their ships when the british requested

Option A. The French crews had sworn allegiance to Germany.

Note: France and British were not at war and such attack was caused by an expectation of danger from German's increasing power.

British were in danger that German's will take control of the French Atlantic ports and French warships therefore they had to make sure to minimize the potential threat.