Answer is (B)
Here in 1st query we are joining Catalog and Supplier and getting pids for all parts which are being supplied.
In 2nd query we are doing same as 1st query but just removing all those rows where Supplier name is not Sachin. i.e., this query returns pids for all parts which are being supplied by any supplier other than Sachin.
In the resulting table we are subtracting 2nd table rows from 1st table and getting pids for those part which are supplied only by Sachin.
If a part is supplied by Sachin and also by some other supplier, it will be selected by the second query and due to "minus" will be missing in the final output. Thus option C is wrong and B is correct.