Q1. What is the passage mainly about?

1. AWhy babies cry at night
2. BHow babies' hearing changes during their first year
3. CHow to teach Japanese to American babies
4. DWhy adults cannot learn English

赤ちゃんのRとLの聞き分けが1歳前後で変わる、という内容なので B。

Q2. What happened to Japanese babies by ten to twelve months?

1. AThey got better at hearing R and L.
2. BThey started speaking English.
3. CThey got worse at hearing R and L.
4. DThey stopped listening to Japanese.

American babies got better, but Japanese babies got worse とあるので C。

Q3. In this passage, "tuned to Japanese" means the babies' ears ...

1. Abecame tired of Japanese
2. Bstopped hearing all sounds
3. Clearned to sing Japanese songs
4. Dbecame good at the sounds of Japanese

tune は楽器などを「調整する」。耳が日本語の音に合わせて調整された＝日本語の音に強くなった、なので D。

Q1. What did the 1984 study find?

1. ABabies could not hear any foreign sounds.
2. BMany younger babies heard foreign sound differences, but older babies mostly could not.
3. COnly Hindi babies could hear the differences.
4. DAdults heard foreign sounds better than babies.

Many six- to eight-month-olds could hear the differences, but by ten to twelve months most of them could not とあるので B。

Q2. From what did babies learn Chinese sounds?

1. AA video of a speaker
2. BAn audio recording
3. CA real person who played with them
4. DTheir parents speaking English

learned Chinese sounds from a real person ... but not from a video or audio recording とあるので C。

Q3. What can we infer from the passage?

1. AJapanese people are born unable to hear R and L.
2. BWatching English videos is enough for babies.
3. CBabies lose all their hearing at age one.
4. DExperience with a language shapes which sounds we can easily hear.

最初は同じでも、聞く言語によって1歳ごろに差が出ることから、経験が聞き取れる音を形作ると推論できるので D。

Q1. Why does the author prefer the word "tuning" to "loss"?

1. ABecause infants' perception of native sounds became sharper at the same time.
2. BBecause babies regain all foreign contrasts at age two.
3. CBecause the studies used musical instruments.
4. DBecause Japanese babies improved on R and L.

because perception of native sounds actually becomes sharper と理由が述べられているので A。

Q2. What did the experiment with Mandarin show?

1. AVideo was more effective than live speakers.
2. BInfants learned nothing from twelve sessions.
3. CLive interaction helped infants keep their sensitivity, but video did not.
4. DOnly adults could learn Mandarin sounds.

twelve play sessions with a live Mandarin speaker で感受性が保たれ、Infants who watched the same material on video did not. とあるので C。

Q3. Which statement would the author most likely agree with?

1. AAdults who struggle with R and L should give up.
2. BEvery baby loses foreign contrasts at exactly ten months.
3. CBabies learn languages best from screens.
4. DAdult learners can still train their ears for difficult foreign sounds.

最終文 With training, adults can still improve their perception of non-native contrasts. と一致するので D。