They put their books____to make the library clean and tidy.

A．under the chair

B．on the floor

C．behind the door

D．in the bookcase

由内地检验检疫机构检疫合格后运到深圳出口的供港猪、牛、羊，必须随附由当地县以上兽医卫生防疫站出具的熏蒸消毒证书。( )