Since the words las muchachas means - the girls, we definitely need a plural verb. There are two plural verbs here - somos and son.
The word somos refers to us - Nosotros somos means We are.
Since the girls are third person plural (they), you need to use the verb B. son.
Las muchachas del club B. son de Estados Unidos y Mexico.
Yo soy, tu eres, el/ella/Usted es, nosotros somos, vosotros sois, ellos/ellas/Ustedes son