Q$2(8$ pt$)$: Given the following relational schema $($attribute types are omitted

for simplicity$)$:

Park$($pid$,$ name, year$)$

Belong$())$

Trail$($tid$,$ tname, length, trail$\_$rating$)$

Answer the relational algebra for the following questions:

$($a$)$ Return all the names of the parks established after $1990$

$($b$)$ Return the name of the park in which all trails are rated greater than $4.$

$($c$)$ Write down the SQL query to solve the question $($a$)$ request.

$($d$)$ Write down the SQL query to solve the question $($b$)$ request.