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if Name is a Primary Key, then S₁ = S₂ = S₃

if (Name,Marks) pair is a primary key ( but not Super key ) , then in general S₁ = S₂.

But if " Deepti " ( the inner query ) has only one marks associated with her, then it leads to S₁ = S₂ = S₃

Answer 1

a will be correct say all girls with name depti has  marks like 10,20 ,30 , 40

Now what inner query will return in all cases is same that is (10,20,30,40)

query 1)

 it will return names of students who has marks 10 or 20 or 30 or 40

Query 2)

return names of students having marks either 10 or 20 or 30 or 40 because IN opertaor will try to see if any case matches ... if any case matches then print it

Query 3)

it will return names of students who has marks equal to all 10 ,20 ,30 ,40

so if a studnets are there who has name RAVI and students having name ravi scored 10 ,40, 20 , 30

then only it will print the result.

So as per query 1 st and 2nd one .