$(21$ pts$)(7$ pts each$)$

Find a regular expression corresponding to each of the following subsets of $\{0,1{\}}^{**}.$

$($a$)$ The language of all strings containing exactly two $0\text{'}$s$.$

$$

$($b$)$ The language of all strings containing at least three $1\text{'}$s $.$

$$

$($c$)$ The language of all strings that do not begin with $00.$