Customers for Prepaid Mobile Telephone Service Pay a Lump Sum

Customers for prepaid mobile telephone service pay a lump sum price for a fixed quantity of usage. Customers for post-paid service enter into a contract that stipulates a monthly subscription charge and price per unit of usage. Customers of pre-paid service tend to consume and spend less than customers of post-paid mobile service. Fill in the blanks: ______ service is an inferior product and ______ service is a normal product.

A) Prepaid, Post-paid.
B) Post-paid, Prepaid.
C) Prepaid, Prepaid.
D) Post-paid, Post-paid.