What Does It Mean When We Say a Stimulus Set

What does it mean when we say a stimulus set, such as the International Affective Picture System, is ""validated"" and ""standardized""?

A) Depending on the individual participant, the stimuli have a range of emotional effects, granting the researcher ample variability in their independent variable
B) The stimuli are highly familiar to the average participant, such as movies most people have seen
C) The stimuli were selected and pretested to ensure that they have the intended emotional effect across participant samples
D) The stimuli will only work for a very specific, ""standard"" participant sample, such as college students