please answer any. or both if u know it$.$ In the Backtracking Algorithm for constraint propagation problems, how does the

function SELECT$-$UNASSIGNED$-$VARIABLE select a variable to work on next? $($Do not write

more than $10$ sentences.$)$

$[15$ points$]$ Give an example of each type of propositional logical sentences below:

$($a$)$ Definite clauses.

$($b$)$ Negative literals

$($c$)$ Conjunctive normal form.