阅读理解
We all have offensive breath at one time or another. In most cases, offensive breath emanates from bacteria in the mouth, although there are other, more surprising causes.
Until a few years ago, the most doctors could do was to counsel patients with bad breath about oral cleanliness. Now they are finding new ways to treat the usually curable condition.
Bad breath can happen whenever the normal flow of saliva slows. Our mouths are full of bacteria feeding on protein in bits of food and shed tissue. The bacteria emit evil-smelling gases, the worst of which is hydrogen sulfide.
Mouth bacteria thrive in airless conditions. Oxygen-rich saliva keeps their numbers down. When we sleep, for example, the saliva stream slows, and sulfide-producing bacteria gain the upper hand, producing classic " morning breath".
Alcohol, hunger, too much talking , breathing through the mouth during exercise — anything that dries the mouth produces bad breath. So can stress, though it''s not understood why. Some people''s breath turns sour every time they go no a job interview.
Saliva flow gradually shows with age, which explains why the elderly have more bad-breath trouble than younger people do. Babies, however, who make plenty of saliva and whose mouths contain relatively few bacteria have characteristically sweet breath.
For most of us, the simple, dry-mouth variety of bad breath is easily cured. Eating or drinking starts saliva and sweeps away many of the bacteria. Breakfast often stops morning breath.
Those with chronic dry mouth find that it helps to keep gum, hard candy, or a bottle of water or juice around. Brushing the teeth wipes out dry mouth bad breath because it clears away many of the offending bacteria.
Surprisingly, one thing that rarely works is mouthwash. The liquid can mask bad-breath odor with its own smell, but the effect lasts no more than an hour. Some mouthwashes claim to kill the bacteria responsible for bad breath. The trouble is, they don''t necessarily reach all offending germs. Most bacteria are well protected from mouthwash under thick layers of mucus. If the mouthwash contains alcohol — as most do — it can intensify the problem by drying out the mouth.
单选题
The phrase " emanate from " in Paragraph 1 most probably means "______".
单选题
Which of the following is mentioned as one of the causes of bad breath?
【正确答案】
D
【答案解析】文章第五段第一句和第二句例举了导致bad breath的种种原因。Alcohol，hunger，too much talking，breathing through the mouth during exercise—anything that dries the mouth produces bad breath．So can stress，though it''s not understood why．酒精、饥饿、说话太多、锻炼时用口呼吸等诸如此类使口腔干燥的因素都会导致口有异味。紧张也可导致如此，不过其原因尚不清楚。四个选择项当中Mental strain心理紧张符合文章内容，正确答案是D。
单选题
According to the passage, alcohol has something to do with bad breath mainly because______.
【正确答案】
D
【答案解析】文章第三段第一句指出：Bad breath can happen whenever the normal flow of saliva slows…当唾液分泌减慢时就会发生口腔异味。第五段第一句还告诉我们酒精可以使口腔干燥，所以我们可以推断酒精会影响唾液的分泌，即D项，正确答案是D。
单选题
Mouthwashes are not an effective cure for bad breath mainly because______.
【正确答案】
B
【答案解析】依据文章第九段第四句The trouble is they don''t necessarily reach all offending germs。麻烦的是他们不能抑制所有有害病毒。可以判断B最符合题意，正确答案是B。