Consider the following relational schema:

Suppliers$($sid:integer, sname:string, city:string, street:string$)$

Parts$($pid:integer, pname:string, color:string$)$

Catalog$($sid:integer, pid:integer, cost:real$)$

Consider the following relational query on the above database:

SELECT S$.$sname

FROM Suppliers S

WHERE S$.$sid NOT IN $($SELECT C$.$sid

FROM Catalog C

WHERE C$.$pid NOT IN $($SELECT P$.$pid

FROM Parts P

WHERE P$.$color$<>$ 'blue'$))$

Assume that relations corresponding to the above schema are not empty. Which one of the following is the correct interpretation of the above query?