21. Customers will receive a free CD as a(n)  _______ with any order over 200 Yuan in this store .

A. payment                B. bonus                       C. reward                     D. benefit

22. Tom accumulated a grate deal of knowledge about plants and agriculture in growing strawberries, he went back to the abandoned          of spreading straw under the fruit to reduce the necessary amount of watering.

A. custom                     B. approach                    C. practice                  D. principle