Q1. What is the passage mainly about?

1. AHow to train a dog
2. BCounting brain cells in dogs and cats
3. CWhy cats hunt alone
4. DWhich pet is easier to keep

イヌとネコの大脳皮質の神経細胞を数えた研究の話なので B。

Q2. About how many nerve cells did the cat have in its cerebral cortex?

1. AAbout 250 million
2. BAbout 430 million
3. CAbout 630 million
4. DAbout two billion

A cat had about 250 million. とあるので A。4億3,000万〜6億3,000万個はイヌの数。

Q3. In this passage, "alone" means ...

1. Awith many friends
2. Bvery quickly
3. Cwithout others
4. Dat night

alone は「ひとりで・単独で」なので C。人と協力するイヌとの対比になっている。

Q1. How were the neurons counted?

1. ABy looking at each cell under a microscope one by one
2. BBy measuring the weight of the brain
3. CBy testing how smart the animals were
4. DBy turning the brain into a soup and counting nuclei in a sample

The brain is dissolved into a uniform "soup," and the nuclei in a small sample are counted とあるので D。

Q2. What was surprising about the brown bear?

1. AIt had the most neurons of all.
2. BIts large cortex had about the same number of neurons as a cat's.
3. CIt had a smaller cortex than a cat.
4. DIt had twice as many neurons as a dog.

cortex is about ten times larger than a cat's, had about the same number of neurons as the cat とあるので B。

Q3. Why does the writer mention that only two dogs and one cat were examined?

1. ATo show that the results should be treated carefully
2. BTo show that the study was very expensive
3. CTo prove that dogs are smarter than cats
4. DTo explain why bears were not included

However に続けて標本の少なさを述べており、結果を慎重に受け止めるべきだと示しているので A。

Q1. Which animal had the most cortical neurons among those examined?

1. AA brown bear
2. BA lion
3. CA golden retriever
4. DA raccoon

630 million in a golden retriever, the highest of any animal examined とあるので C。

Q2. What does the passage say about cortex size and neuron number?

1. AThey always increase together.
2. BLarger cortexes always contain fewer neurons.
3. COnly cats show a link between them.
4. DA bigger cortex does not necessarily contain more neurons.

Cortex size and neuron number did not rise together とあり、ライオンやヒグマの例が挙げられているので D。

Q3. Why does the author hesitate to conclude that dogs are smarter?

1. ABecause the samples were tiny and neuron counts do not directly measure intelligence
2. BBecause cats had more neurons than dogs
3. CBecause the counting method was proven wrong
4. DBecause dogs and cats were not included in the study

Only two dogs and one cat were studied とあり、さらに More neurons may also raise a brain's capacity without deciding how intelligent an animal is と述べているので A。