Scientists hope that if we can discover __21__ the brain works, the better use we will be able to put it to. For example, how do we learn language? Man differs most from all the animals in his ability to learn and use language __22__ we still do not know exactly how this is done. Some children learn to speak and read and write when they are very young compared to __23__ children. But scientists are not sure why this happens. They are trying to find out __24__ there is something about the way we teach language to children which in fact prevents children __25__ learning sooner..8888
选项：

A: but
B: how
C: from
D: whether
E: average