A cable TV company is considering offering optical fibre to residences to improve the speed of its movie download service. Before launching the new service, however, the company wants to find out whether customers would pay the \(\$ 50\) per month that the company wants to charge. An intern has prepared several alternative plans for assessing customer demand. For each, indicate what kind of sampling strategy is involved and what (if any) biases might result.

a) Put a big ad in the newspaper asking people to log their opinions on the company's website.
b) Randomly select one of the towns and contact every cable subscriber by phone.
c) Send a survey to each customer and ask each of them to fill it out and return it.
d) Randomly select 20 customers from each town. Send them a survey, and follow up with a phone call if they do not return the survey within a week.