Answer:
e. National Do-Not-Call Registry
Explanation:
National Do-Not-Call Registry -
It enables the users to get the choice of whether receive any telemarketing calls or not , is referred to as National Do-Not-Call Registry .
People can get registered here for free to select his or her choice .
Hence, from the question,
Gutter guy are switching the telemarketing to direct mail so as to avoid the National Do-Not-Call Registry .