Within a document, which of the following specifies that an individual must digitally sign the document?

A(n) ________ distribution takes on the shape of a bell and is often referred to as the "bell-shaped curve."

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

Using square brackets ([]) to retrieve vector elements __________ perform bounds checking; using member function at to retrieve vector elements __________ perform bounds checking.

a. Does not, does not. b. Does not, does. c. Does, does not. d. Does, does.