they are nurses改为单数形式

they are nurses改为单数形式 they are apples改为单数 they are waitresses(改为单数 把They are apples.改为单数句 Are they students?（改为单数句） What colour are they?改为单数句 are they apples?改为单数形式 they are English books.(改为单数形式) Are they American cars?改为单数 为啥 They are his friends改为单数形式 Are they bookcase 怎样改为单数句? are they american students?改为单数形式 They are my friends.改为单数句 They are English cars.(改为单数形式) Are they women doctors? 改为单数句 they are old computers改为单数形式 Are they English girls?改为单数. Are they American cars?（改为单数）