What Have Researchers Typically Found When They Have Attempted to Demonstrate

What have researchers typically found when they have attempted to demonstrate subliminal perception effects in the real world

A)  Such effects are substantial and a potential cause for public concern. 
B)  People are much more likely to be influenced by "positive" subliminal stimuli (e.g., self-help tapes) than "negative" ones (e.g., subliminal advertising) . 
C)  People are much more likely to be influenced by "negative" subliminal stimuli than "positive" ones. 
D)  Such effects are so weak as to be of little, if any, practical importance.