In the Study Using the Visual Cliff and 12-Month-Olds

In the study using the visual cliff and 12-month-olds,

A) the majority of the babies refused to cross to the "deep" side.
B) none of the babies crossed to the deep side even when their mothers displayed happiness.
C) only the babies with easy temperaments crossed to the "deep" side.
D) it was not clear whether the babies were responding to their mothers' facial expressions or the loudness of their voices.