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 PLEASE HELP ME
How would you tell a group of people to prepare for a hurricane?

A. Preparan para un huracan.

B. Prepara para un huracan.

C. Preparense para un huracan.

D. Prepare para un huracan.

I am almost for sure you need to use the imperative form of the verb preparar but I can't decide between B and D. I still have a bit of trouble choosing ustedes vs tu for the verb. Help would be appreciated.