Prior to HTML5, the ____ element was used almost exclusively to mark headers, footers, asides, and other named sections.

Which of the following is not a valid identifier?

a) Pig3 b) I_HAVE_A_DOG c) help! d) _answer

A(n) ____________________ provides a list of alternative fonts; if the first font is not available, it will try the next font in the list.

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