Which of the choices below do not complete the following sentence correctly? A _________ is a ___________.

__________ prevents either sender or receiver from denying a transmitted message. Thus, when a message is sent, the receiver can prove that the alleged sender in fact sent the message and when a message is received, the sender can prove that the alleged receiver in fact received the message.

Fill in the blank(s) with the appropriate word(s).

If a table is created and it is later determined that additional fields should be added to the table, it is usually preferable to

a) delete the existing table and re-create it with the additional fields b) create a parallel table that holds just the additional fields c) re-define an existing field in the table to hold the additional data d) delete the entire database and start over e) alter the table to add the additional fields