Rosie wrote this expression to describe the amount she paid for each yoga class. 30 / m Which situation could be described by this expression?
   A. Rosie knows that each yoga class costs $30. She doesn't know how many classes she bought.
   B. Rosie knows that she paid $30 for one yoga class. She does not know the total amount she spent.
   C. Rosie knows that she paid a total of $30 for the yoga classes. She doesn't know how many classes she's gone to so far.
   D. Rosie knows that she paid a total of $30 for the yoga classes. She does not know how many classes she bought.