Thank you very much for sending us your latest catalogue and price list（）21 January.

Thank you very much for sending us your latest catalogue and price list（）21 January.
正确答案：on
解析:本题考查介词 on 表示日期的用法。全句意思是：非常感谢贵公司在1月21日给我方寄送的最新产品目录和价目表。