DBA$-221$True or False and why?

$17.$The REPEAT UNTIL loop continues until an expression evaluates as false.

$18.$ STRICT$\_$TRANS$\_$TABLES is the most restrictive "strict" mode.

$19.$ The $\text{'}$@$\text{'}$ symbol is optional when declaring and using user variables.

$20.$ Built$-$in functions can be used in any statement that accepts an expression, except SET statements.

$21.$ You can give variables an initial value with the DEFAULT clause and assign a new value using the SET statement.

$22.$ Used correctly, stored programs can improve the performance, security, maintainability, and reliability of applications.

$23.$ A function may not return a result set.

$24.$ Conditional expressions may evaluate to TRUE, FALSE, or NULL$($unknown$).$