When encouraged to eat as much as they want, people tend to eat less if the foods are offered in smaller, rather than in larger, containers, illustrating the relevance of:
a) social facilitation.
b) portion size.
c) the yerkes-dodson law.
d) the spillover effect.

B) portion size.

Explanation:

Large portions of food lead people to eat beyond necessity. It may seem obvious that the larger the portion size, the more people eat, but, until this systematic review, the evidence for this effect had been quite fragmented, so the overall picture so far has been unclear. However, we know that portion size is very relevant in relation to the amount of food eaten. That's because when encouraged to eat as much as they like, people tend to eat less if food is offered in smaller rather than larger containers.

c it has to be i googled it