Delete duplicates based on two collumns

Hi,

I have a big spreadsheet containing costumers purshases for a period. The same customer generally purshased the same product more than once. I need to eliminate all the duplicate lines based with the same value on 2 collumns, the customer (B) and the product (D) in order to keep only one line for each product that the customers purshased.

Thanks for helping...

Simon