Answer:
Subject: Rhett and Charlie
Verb: sing
Step-by-step explanation:
The verb of a sentence is the word that presents an activity that is being practiced, thus, we can conclude that the word "sing" represents an activity, being then, the word "sing" a verb.
The subject of a sentence is the word that represents the people or objects that are exercising the activity presented by the verb. In the sentence above, we can see that Rhett and Charlie are singing, so they are both the subjects of the sentence.