1. During a single crucial three-week period during our teenage years, chemical activity in the brain is cut in half.
    我们的青少年阶段有一个为期三周的关键时期，此时脑部的化学反应活动一分为二。

2. A single spark can start a prairie fire.
    星星之火, 可以燎原。

3. As a single man he had never troubled much if he happened to be out of work; but now that he was married it was different: the fear of being "out" haunted him all the time.
    他过单身生活时，即使偶尔失了业，他也未太烦恼过。可是，既然结了婚，情况就不同了，失业的恐惧时刻都在困扰着他。

4. As we drove along, someone would single out to me a famous building, an important street, a park, a bridge that when built was thought to be a landmark.
    当我们驱车行驶的时候，有人指给我看那些建造时被曾认为是陆上的标志性建筑物：著名大楼、重要街道，公园和大桥。

5. "The movements are very slow and careful and involve a great deal of body movement and standing on a single limb.
    它的动作缓慢、细腻，动则牵引全身，立则依附单腿。

6. A single tree may seem large compared to a person.
    和人相比，一棵树看起来很大。

7. An immediate search over 100,000 square miles of sea failed to turn up a single piece of the missing plane.
    随后立即展开了范围宽达100,000平方英里的海面搜索，但没有发现一片失踪飞机的残骸。

8. A single gene will code for only one of the many molecules and cell proteins that are the building blocks of the brain.
    一个基因仅仅为构成大脑的众多分子和细胞蛋白中的一个指定遗传密码。

9. You'll find it easier, then, to keep from settling for the single piece of candy.
    那样，你就不会轻易满足于只吃一块糖了。

10. — Children in single-parent households — usually families with only a mother present — are much more likely to be overtaken by poverty than those who live with two parents, largely because of the loss of support from the fathers.
    ——单亲家庭——通常是只有母亲的家庭——的孩子，较之与双亲一起生活的孩子，更可能遭受贫穷，这主要是因为缺少父亲的经济支持。