单项选择题
（）is not a physical wall, but a lot of virtual data to protect the computer network.
A.Data wall B.Data Channel C.Data base D.firewall
单项选择题 （） is meant to provide facility for customer’s need or inquiry and arrange it.
单项选择题 Saving or reducing expenditure in business is （）
单项选择题 （）is guaranteed by the full market supply and Just in time ( JIT ) .
