For each item, write a single regular expression that matches that item. Note that in ALL cases, the entire string must match without additional characters.

A string of digits that contains only digits and contains exactly two fives. Examples of acceptable strings include: $"15445","55","05563"$

The string should be rejected if it contains anything other than a digits.

A regular expression that matches a time expressed in the form $"1$:$45$ PM$".$

The hours part must be a number from $1$ to $12,$ the minutes range from $00$ to $59,$ and the time must indicate either AM or PM $($uppercase only and preceded by exactly one space$).$

A regular expression that matches a string representing a comma separated list of variable names such as: hello, get$\_$max, sum$3$

A variable name consists of letters, digits, and underscores but cannot start with a digit.

There is exactly one space after every comma. No other spaces are allowed.

Commas and spaces are not allowed before the first name and after the last name.

An empty string is considered a match.