Answer:
"You"
Step-by-step explanation:
The sentence given is an imperative sentence because it gives a command. This type of sentence is used to make requests or to give suggestions, advice, or commands, and they almost never mention the subject because it is always implicitly stated: they are always directed to the second person "You", either plural or singular. So, if someone tells you "Hang this garland of flowers around the top of the float" the subject is always you.