被动语态,不用bychange these sentences into passive voice.but DON'T

library books must be returned within three weeks。 再问： 2。You should keep all medicine in a locked cupboard。 3。Customers cannot exchange goods without a receipt。 4。Patients should not take these pills more than twice a day。 5。They may hoist the typhoon signal NO。8 later today。 6。We will not allow children wearing school uniforms into Internet cafe。 7。Can people use this shampoo every day? 再答： all medicine should be kept in a locked cupboard goods cannot be exchanged without a receipt these pills should not be taken more than twice a day。 the typhoon signal NO。8 may be hoisted later today children will not be allowed to wear school uniforms into Internet cafe can this shampoo be used every day? 要休息啦，有问题，再重新发问吧，有别的哥哥姐姐帮你解答啦