作者在短文中多次使用need和important等词汇，还使用了一系列同义词或相关词、反义词或对应词等，如：

(1)teachers—adults;

(2)young adults—typical teenage lifestyle—teenagers—young teens—students;

(3)emotional, intellectual and physical changes—growing bodies—new bodies—new intellectual and emotional challenges;

(4)achieving success—accomplishment—winners—successful;

(5)plan activities—a variety of small clubs—some kind of organization—organization—a variety of activities—organized;

(6)winners—losers 等。

借助这些相关词组成的语意链我们可以更好地把握主题：教师应针对青少年的特点组织活动以帮助学生们成长。

请注意2005年的短文中黑体字和斜体字的提示：

The human nose is an underrated tool. Humans are often thought to be insensitive smellers compared with animals, but this is largely because, unlike animals, we stand upright. This means that our noses are limited to perceiving those smells which float through the air, missing the majority of smells which stick to surfaces. In fact, though, we are extremely sensitive to smells, even if we do not generally realize it. Our noses are capable of detecting human smells even when these are diluted to far below one part in one million.

Strangely, some people find that they can smell one type of flower but not another, whereas others are sensitive to the smells of both flowers. This may be because some people do not have the genes necessary to generate particular smell receptors in the nose. These receptors are the cells which sense smells and send messages to the brain. However, it has been found that even people insensitive to a certain smell at first can suddenly become sensitive to it when exposed to it often enough.

The explanation for insensitivity to smell seems to be that the brain finds it inefficient to keep all smell receptors working all the time but can create new receptors if necessary. This may also explain why we are not usually sensitive to our own smells—we simply do not need to be. We are not aware of the usual smell of our own house, but we notice new smells when we visit someone else's. The brain finds it best to keep smell receptors available for unfamiliar and emergency signals such as the smell of smoke, which might indicate the danger of fire.

本文分析了人们为什么低估人类鼻子作为嗅觉工具的灵敏性，共分三个自然段，除反复出现与“低估人类嗅觉”和“人类实际嗅觉能力”有关的文字外，每段都有表示原因的句型。第一段斜体字 are often thought to be insensitive smellers和 do not generally realize it等指出人们“人类的嗅觉不如动物灵敏”的认识误区。紧接段首句的but this is largely because句型提出产生错误看法的原因：“人类直立行走；”并以表示转折和强调的连接词引入与人们常识不符的事实：“然而，事实上我们的嗅觉是极为灵敏的，即使人们一般都没有意识到这一点。”第二段同样分析为什么有些人似乎对某些气味不够灵敏，做出解释之后同样用事实说明不应低估他们的嗅觉能力，这些人的嗅觉会“突然变得敏感起来”。第三段以The explanation for insensitivity to smell seems to be that…和This may also explain why…