At What Point During the Experimental Situations Did Ainsworth Believe

At what point during the experimental situations did Ainsworth believe the best indicator of the quality of attachment occurred?

A) when the mother was not present in the room
B) when the mother was still in the room, so that the toddler's exploration behaviors could be assessed
C) when the mother returned and the reunion behavior could be assessed
D) before the assessment began; the experimenters could measure toddler-mother behaviors before the mothers knew they were being assessed