Which of the following income may enjoy a reduced tax or exclusion

A．uses letters as a chief means of providing information
B．sends old customers detailed information about new products
C．uses letters to tell prospective buyers about the local sellers
D．sends over the prospective buyers sample products by parcels

A．includes all forms of sales appeals to the prospective buyer
B．is produced mainly for newspaper or television
C．is an activity by which real products are shown to buyers
D．uses post as a chief means to contact prospective buyers