Q1. What is the passage mainly about?

1. AHow to make good coffee
2. BCoffee and long life: what the studies show
3. CWhy coffee is expensive
4. DHow many people live in America

コーヒーと長生きの関係を調べた研究と、その読み方がテーマなので B。

Q2. How long did the American scientists study the people?

1. AAbout one year
2. BAbout five years
3. CMore than 10 years
4. DMore than 40 years

studied about 400,000 people for more than 10 years とあるので C。40万という人数と混同しないこと。

Q3. In this passage, "tended to" means ...

1. Anever did
2. Bhad to
3. Cwanted to
4. Dusually did, but not always

tend to ～ は「～する傾向がある」。必ずではないが多くの場合そうだった、という意味なので D。

Q1. What is the passage mainly about?

1. AWhy coffee studies show a link but not a cause
2. BA new coffee that helps people live longer
3. CHow to stop drinking coffee
4. DDifferences between Japanese and American coffee

大規模研究で関連は見られるが、観察研究なので they do not show that coffee is the cause（原因とは言えない）という内容なので A。

Q2. Which statement about the 2012 study is true?

1. AIt included about 90,000 Japanese people.
2. BResearchers told people how much coffee to drink.
3. CIt followed about 400,000 Americans for over ten years.
4. DIt found that coffee drinkers had a higher risk of death.

followed about 400,000 Americans aged 50 to 71 for more than ten years とあるので C。9万人は日本の研究。

Q3. Why might sick people appear to drink less coffee?

1. ABecause coffee is more expensive for them
2. BBecause they may stop drinking it because of their health
3. CBecause they all live in Japan
4. DBecause coffee causes illness

imagine someone who becomes ill and gives up coffee とあり、体調のせいで飲むのをやめている可能性（逆の因果）が示されているので B。

Q1. What is the author's main point?

1. ACoffee has been proven to extend life.
2. BCoffee is harmful to older people.
3. CStudies link coffee to longer life, but they cannot prove coffee is the cause.
4. DJapanese and American studies disagree about coffee.

So the studies link coffee to longer life without showing that coffee is the cause が主張のまとめなので C。

Q2. Which of the following is an example of reverse causation in the passage?

1. APeople with health problems drinking less coffee
2. BCoffee drinkers having more active social lives
3. CResearchers adjusting for smoking
4. DDrinking three to four cups a day

People with health problems may cut back on coffee ... This is called reverse causation. とあるので A。B は交絡（confounding）の例。

Q3. Why does the author say a randomized trial is "hardly realistic"?

1. ABecause coffee is too expensive to give away
2. BBecause nobody drinks coffee for decades
3. CBecause observational studies are always better
4. DBecause it would require controlling people's coffee drinking for decades

a randomized trial in which people were assigned to drink coffee or avoid it for decades とあり、何十年も飲む・飲まないを割り当てる必要があるからなので D。