Riddles

The 4 element crystals, Air, Fire, Water, and Earth, have been stolen by 4 thieves. Fortunately, you caught them stealing your crystals. The 4 thieves each swallowed their crystal but you don't know who swallowed which crystal. The thieves started to blame each other for swallowing which crystal. Person A says that Person B swallowed the Water Crystal, Person B says that Person C swallowed the fire crystal, Person C says that Person D ate the air crystal, and Person D says that Person A didn't eat the earth crystal. You know that whoever ate the fire and air crystals must lie and the ones who ate the water and earth crystals must tell the truth. Who ate which crystal?