Three other explanations seem more promising. One involves physiological changes relevant

Three other explanations seem more promising. One involves physiological changes relevant to memory. Maturation of the frontal lobes of the brain continues throughout early childhood, and this part of the brain may be critical for remembering particular episodes in ways that can be retrieved later. Demonstrations of infants and toddlers long-term memory have involved their repeating motor activities that they had seen or done earlier, such as reaching in the dark for objects, putting a bottle in a dolls mouth, or pulling apart two pieces of a toy. The brains level of physiological maturation may support these types of memories, but not ones requiring explicit verbal descriptions.

The word "critically" in the passage is closest in meaning to

A．fundamentally

B．partially

C．consistently

D．subsequently

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