Answer:
Both scenario A and D.
Step-by-step explanation:
The study examining infants' ability to do simple arithmetic that showed infants one or two dolls and then either added or subtracted a doll from behind a screen demonstrated that infants were surprised in which of A: A doll is placed behind a screen where another doll was initially present, and lowering of the screen reveals a single doll and D: A doll is removed from behind a screen where two dolls were initially present, and lowering of the screen reveals two dolls.