There is no dog in Nick's family because ...

1. Nick's family prefers dogs but doesn't have one. 2. They have a cat named China. 3. The text implies they might not have time for a dog due to work and tennis. However, the most direct reason implied by the text is that they prefer dogs but haven't gotten one yet, possibly due to time constraints or other unstated reasons. The options provided are limited. Considering the options, 'they don't like dogs' is false. 'they have got a cat' is true but not the reason for not having a dog. 'they have not got time to look after a dog' is the most plausible reason given their busy schedules. However, the text states 'We prefer dogs. But we haven't got one because my parents both work and I spend a lot of time at school and play tennis after school.' This directly links not having a dog to their busy schedules. Therefore, the best answer is that they don't have time to look after a dog.
Answer: they have not got time to look after a dog.