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Most people do not get enough fiber (纤维) in their daily diet. Only about 5% of adults get the right amount — 25 grams for women and 38 grams for men. The average person eats only about 17 grams per day.

What exactly is fiber? It is the part of plant foods that our body cannot digest. Our stomach and small intestine (小肠) cannot break it down, so it passes into our large intestine (大肠). There, tiny bacteria (细菌) feed on it. These bacteria break down fiber and turn it into things that help protect us from diseases. Without enough fiber, our body cannot work well, and we may feel uncomfortable. That’s why getting enough fiber is so important.

How can we get more fiber? Small changes can make a big difference. For example, eat whole wheat bread instead of white bread. Add some fruit to your breakfast like an apple or a banana. Choose nuts or vegetables as a snack instead of chips. Also, drink plenty of water every day, because fiber needs water to work in our body.

While you can take fiber supplements (补充剂), experts say eating fiber from natural food is a better choice. Supplements often contain only one type of fiber, but whole foods provide many nutrients that work together to keep us healthy. Whole fruits, vegetables and grains are the best sources — and they are easy to find in our daily life.

1.1.How much fiber does a 23-year-old man need each day?

A 17 grams.

B 25 grams.

C 38 grams.

D 5 grams.

解析：选C。C细节理解题。根据第一段原文“25 grams for women and 38 grams for men”（女性25克，男性38克），23岁男性属于成年男性，每日需要38克纤维。A项17克是普通人实际摄入量（张冠李戴）；B项25克是女性推荐量（张冠李戴）；D项5%是达标成年人比例，不是克数（张冠李戴）。故选C。

2.2.The word “digest” in paragraph 2 probably means ______.

A combine food

B break down food

C search for food

D push out food

解析：选B。B词义猜测题。根据第二段原文“Our body cannot digest it. Our stomach and small intestine cannot break it down”，下句中“break it down”是对digest的解释说明（同义复现），可推断digest意为“分解食物”。A项“合成食物”、C项“寻找食物”、D项“排出食物”均与此处语境不符，属无中生有。故选B。

3.3.What can we infer from paragraph 3?

A White bread has more fiber in it.

B Water stops fiber from working well.

C Simple changes add more fiber.

D Only vegetables are good sources.

解析：选C。C推理判断题。根据第三段原文“Small changes can make a big difference”及后续举例——“eat whole wheat bread instead of white bread”、“choose nuts instead of chips”，这些例子都是“简单替换”（simple changes），可推断简单的替换就能增加纤维摄入。A项“白面包纤维更多”与原文“instead of white bread”（用全麦代替白面）矛盾，属颠倒是非；B项“水阻碍纤维工作”与原文“fiber needs water”矛盾，属颠倒是非；D项“只有蔬菜是好的来源”以偏概全，原文还提到了水果和坚果，属以偏概全。故选C。

4.4.What does the writer think of whole foods?

A They work better than supplements.

B They are too expensive to buy.

C They have very little fiber in them.

D They are hard to find in stores.

解析：选A。A观点态度题。根据第四段原文“experts say eating fiber from natural food is a better choice”以及“whole foods provide many nutrients that work together to keep us healthy”，可知作者认为全食物比补充剂更好。B项“太贵”、C项“含纤维极少”、D项“难买到”文中均未提及，属于无中生有。故选A。

5.5.What is the best title for the passage?

A How Bacteria Help Our Body

B Why We Need More Fiber

C Where to Find Healthy Snacks

D Supplements for Your Health

解析：选B。B主旨大意题。全文围绕纤维展开：P1指出摄入不足的问题 → P2解释纤维是什么及为什么重要 → P3给出增加纤维的方法 → P4对比全食物与补充剂。各段共同回答：膳食纤维为什么重要。A项“细菌如何帮助消化”只覆盖P2，属以偏概全；C项“哪里找健康零食”只覆盖P3一部分，属以偏概全；D项“为健康补充剂”只覆盖P4，属以偏概全。故选B。