Refer to the Following Paragraph to Answer the Questions Below

Refer to the following paragraph to answer the questions below.
Robert Warner, president of a local TV station, recently conducted a study of TV viewers in his area. He obtained a list of all residential customers from the cable TV company billing list. Oddly enough, he put every customer name on a 3x5 note card, and mixed them up in one raffle barrel. He then choose 1000 note cards out of a possible 20,000 customer cards) . A trained interviewer visited each household and asked detailed questions about the viewing habits of various family members.
-How large is his sampling ratio?

A) 1/200
B) 1/20
C) 1/10
D) 3/2,000