11. Express these system specifications using the propositions p: "The message is scanned for viruses," and q: "The message was sent from an unknown system" together with logical con- nectives (including negations). (a) "The message is scanned for viruses whenever the message was sent from an unknown system." (b) "The message was sent from an unknown system but it was not scanned for viruses." (c) "When a message is not sent from an unknown system it is not scanned for viruses."