试题分析：这篇文章主要讲了语言学习可以提高你的智力，语言学习对大脑的促进作用比作体育锻炼能促进肌肉健全，说明语言学习对大脑的促进有类似的作用。

1．C主旨大意题。作者在第一段中就提出了本文的主题，然后下文围绕这一主题进行深入地阐述，即“语言学习可以提高你的智力”。故选C。

2．C词义猜测题。根据本词前后的解释“They were compared with a group of ‘early bilinguals' who had learnt a second language before the age of five, as well as a number of later learners.”，可知其意思应是“a person who can speak two languages”。故选C。

3．A推理判断题。根据Scans showed that grey matter density (密度) in the brain was greater in bilinguals than in people without a second language. The results showed that the younger they started to learn, the better.可知学习第二语言越早，灰质密度越大。故选A。

4．B段落大意题。根据文章大意，作者在最后两段继续阐明其中心论点，即外语学习宜早不宜迟。可知故选B。