Q1. What is the passage mainly about?

1. AWhether it is too late to learn English as an adult
2. BHow to make an online quiz
3. CWhy children like grammar
4. DHow many people speak English

英語は子どものうちに始めないと手遅れか、という問いへの研究の答えがテーマなので A。

Q2. Until about what age does the ability to learn grammar stay high?

1. AAbout 10
2. BAbout 7
3. CAbout 17
4. DAbout 67

the ability to learn grammar stays high until about age 17 とあるので C。10歳はネイティブ並みを目指す場合の開始年齢の目安。

Q3. In this passage, "too late" means ...

1. Avery early in the morning
2. Ba good time to begin
3. Cafter school
4. Dpast the time when something can be done

too late は「遅すぎる・手遅れ」。もう間に合わない時期という意味なので D。

Q1. What is a "critical period" for language?

1. AA time when people speak too quickly
2. BA period of exams at school
3. CAn age after which learning a new language becomes much harder
4. DThe time it takes to finish a grammar quiz

After a certain age, learning a new language becomes very difficult. と説明されているので C。

Q2. What does the passage say about classes with only a few hours of English a week?

1. ANobody can learn English in such classes.
2. BOlder beginners often progress faster.
3. CYounger children always do better.
4. DGrammar is not taught at all.

older beginners often make faster progress than younger ones とあるので B。

Q3. What can we infer from the passage?

1. AAdults should give up learning English.
2. BStarting early guarantees perfect English.
3. CThe study proves that school English is useless.
4. DStarting late may limit native-like grammar, but it does not stop people from learning.

10歳ごろまでに始めることが大事なのはネイティブ並みの文法の場合だけで、年上の学習者が速く伸びる例も挙げているので、遅く始めても学べると推論できる。正解は D。

Q1. What was surprising about the 2018 study's estimate?

1. AGrammar-learning ability declined later than many had assumed.
2. BNobody could learn grammar after age 10.
3. CNative speakers did worse than learners.
4. DGrammar-learning ability never declined.

stays high until about age 17 and then gradually declines, later than many had assumed とあるので A。

Q2. Which of the following is mentioned as a limitation of the 2018 study?

1. AIt included only children.
2. BIt measured only pronunciation.
3. CIt was done in one small classroom.
4. DIt relied on cross-sectional data and model assumptions.

The data were also cross-sectional, so the estimates depend on model assumptions instead of on following individuals over time とあるので D。測ったのは文法で、発音は測っていない。

Q3. What did the 2021 reanalysis argue?

1. AThe original data were fake.
2. BThe pattern fits a steady decline better than a sudden drop.
3. CAdults learn grammar faster than children in all settings.
4. DThere is no relationship between age and learning.

for most groups the pattern fits a steady decline better than a sudden drop at 17 とあるので B。