脳は「2つの臓器」だった？ 脳の前と後ろは、別々の細胞から生まれていた

Q1. What is the passage mainly about?

1. AWhere the parts of the brain come from
2. BHow mice sleep
3. CHow to keep your heart healthy
4. DWhy people like to think

脳の前と後ろがどの細胞グループから始まるか、という話なので A。

Q2. What does the back part of the brain control?

1. ALanguage and math
2. BOur favorite colors
3. CBreathing, heartbeat, and sleep
4. DOur memories of school

The back part controls breathing, heartbeat, and sleep. とあるので C。

Q3. "Scientists used to think ..." means that scientists ...

1. Awill think so in the future
2. Bthought so in the past, but the idea is now changing
3. Cnever thought so
4. Dthink so every day

used to ～ は「以前は～していた（今は違う）」。直後の But a new study ... shows something different とも合うので B。

Q1. What did scientists believe for a long time?

1. AThe brain has no front or back.
2. BMice and humans have the same brain.
3. CThe hindbrain develops first.
4. DThe whole brain came from a single group of cells.

第1文 scientists believed that the whole brain developed from a single group of cells とあるので D。

Q2. Which part controls breathing and heart rate?

1. AThe forebrain
2. BThe hindbrain
3. CThe midbrain
4. DThe whole embryo

the hindbrain, which controls basic functions such as breathing and heart rate とあるので B。

Q3. Why might the new finding be useful for medicine?

1. AIt shows that ALS can be cured.
2. BIt proves that mice can get ALS.
3. CIt helped the team make hindbrain nerve cells that were hard to produce.
4. DIt means people no longer need a hindbrain.

作るのが難しかった後脳の神経細胞を作れ、病気の研究に役立つかもしれない（may help research）と述べているので C。「治る」とは書いていない。

Q1. What is the author's attitude toward the headlines?

1. AThey exaggerate the findings somewhat.
2. BThey are completely accurate.
3. CThey understate the importance of the study.
4. DThey are unrelated to the research.

見出しに対し、研究は makes a narrower claim とし、They do not say it is two separate organs と述べているので、見出しはやや誇張という立場。正解は A。

Q2. According to the passage, which gene is expressed in the cells that form the hindbrain?

1. AOtx2
2. BBoth Otx2 and Gbx2
3. CNeither gene is mentioned
4. DGbx2

The other expresses Gbx2 and forms the hindbrain とあるので D。Otx2 は前脳・中脳側。

Q3. Which of the following is a limitation mentioned in the passage?

1. AThe study used only adult humans.
2. BMost evidence comes from mouse embryos and cultured cells.
3. CThe researchers could not grow any neurons.
4. DNo other animals were examined.

Their main evidence comes from mouse embryos and cultured cells rather than human fetuses とあるので B。ヒトの胎児で直接確かめてはいない。