display results from Table were a column satisfies having only these.

Would like to explian further with below example i am using MS SQL Server

I have 2 Table TableA and TableB

TableA

ID	Country
1	Indonesia
2	Singapore

TableB

SupplierID	TableA_ID
4	1
4	2
3	1
2	2

Now i want to select column SupplierID from TableB only where TableA_ID = 1 and 2

The result that i want to be displayed is SupplierID = 4

The problem that i am facing is if i use WHERE IN (1,2) condition other SupplierID are also displayed, can anyone help me how shall i put Query so i get desired results.

Please let me know if above was not clear.