【单选题】

It is, everyone agrees, a huge task that the child performs when he learns to speak, and the fact that he does so in so short a period of time challenges explanation.

Language learning begins with (26) . Individual children (27) greatly in the amount of listening they do before they start speaking, and (28) starters are often long listeners. Most children will "obey" spoken (29) some time before they can speak, though the word obey is hardly (30) as a description of the eager and delighted cooperation usually shown by the chilD、Before they can speak, many children will also ask questions by (31) and by making questioning noises.
Any (32) to trace the development from the noises babies (33) to their first spoken words leads to (34) difficulties. It is (35) that they enjoy making noises, and that during the first few months one or two noises (36) themselves out as particularly (37) of delight, distress, sociability, and so on.But since these cannot be said to show the baby’s intention to (38) , they can hardly be regarded as early forms of language. It is agreed, too, that from about three months they (39) with sounds for enjoyment, and (40) by six months they are able to add new sounds to their (41) . This self-imitation leads on to (42) imitation of sounds made or words spoken to them (43) other people. The problem then (44) as to the point at (45) one can say that these imitations can be considered as speech.
A．when
B．that
C．which
D．where