Final answer:
The foot-in-the-door technique is effective because people tend to agree to small requests first, thereby increasing their likelihood of agreeing to larger requests later due to the principle of consistency.
Step-by-step explanation:
Researchers believe that the foot-in-the-door technique is effective because people have a tendency to agree to small requests first, as option A suggests. The technique works by initially getting a person to consent to a minor request, which then increases the likelihood they will agree to a more significant request later. This method is rooted in the principle of consistency, which suggests that once we commit to a behavior, we prefer to maintain that commitment. For example, in sales, a customer who agrees to add a small item or service (like a basic data plan for their phone) may later be convinced to agree to a larger purchase (such as an extended warranty).