We just have to think which table would be in the outer loop. To minimize block accesses, we have to put that table outside having fewer records because for each outer record, one block access inside will be required.
Therefore, putting $2$nd table outside,
- for each of $400$ records
- $80$ block accesses in the first table $ \implies 32000$ accesses.
- $20$ block accesses of the outer table.
So, the answer comes out to be $32000+20 = 32020$
Correct answer: C.