阅读下列短文，从短文后各题所给的A、B、C、D四个选项中，选出可以填入空白处的最佳选项。Many idioms (习语) in English are based on 1 .
Many American families have a pet dog, which makes children feel happy. But for some reasons, Americans use "dog" in a phrase that means to feel unwell. If you are as 2 as a dog, you will be most likely to have to stay at home and rest, or even go and see a doctor.
Besides dogs, cats are also beloved family members in US families. Sometimes you may hear them 3 in American's conversations. "I told you to keep that a secret, but you have just let the cat out of the bag!" You probably have guessed it — that idiom means to uncover a secret or tell facts that were unknown before.
Dogs and cats don't always 4 well, but they appear together in a commonly used idiom. When it rains 5 , people might say it's raining cats and dogs outside.
