6、heyhavegonetoShanghai.A.MaryandPeter'sB.MaryandPeterC.Mary'sandPeterD.Mary'sandPeter's17.Theteacherwants .A.threepiecesofchalkB.threepieceofchalkC.threepiecesofchalksD.threepieceofchalks18.Nohurry!Westillhave time.A.alotB.fewC.plentyofD.many19.---Goodmorning,madam.CanIhelpyou?---Sure,I'dlike for