There are four hotels competing with otherwise very similar products on the dimensions of price ($ per night) and amenities (measured by the number of *s awarded by customer reviews). 

Hotel A: price = $200 per night; rating: *** 

Hotel B: price = $150 per night; rating: **** 

Hotel C: price = $300 per night; rating ***** 

Hotel D: price = $80 per night; rating ** 

Which of these hotels are on the efficient frontier? You may select more than one answer.