The answer is "b. foot in the door".
Professor Leeds has used "foot-in-the-door technique".
Foot-in-the-door or as known for short “FITD” technique is a compliance strategy that goes for getting a man to consent to a substantial demand by having them consent to an unobtrusive demand first. The foot-in-the-door strategy succeeds attributable to a fundamental human reality that social scientists call "successive approximations".