- Thick fur is a kind of fur
- Fur is a part of skin for keeping warm
- So, thick fur can be used for keeping warm

- An animal is a kind of living thing
- If a living thing becomes too cold then that living thing will die
- Therefore, if an animal becomes too cold then that animal will die

- If an animal becomes too cold then that animal will die
- Keeping warm is the opposite of becoming cold
- So, an animal requires warmth for survival

- An animal requires warmth for survival
- If the environmental temperature is too cold then an animal in that environment may become cold
- Therefore, an animal requires warmth for survival in cold temperatures

- Thick fur can be used for keeping warm
- An animal requires warmth for survival in cold temperatures
- So, thick fur is used by animals for keeping warm in cold temperatures

- Thick fur is used by animals for keeping warm in cold temperatures
- Winter has cold temperatures
- Hence, thick fur is used by animals for keeping warm in winter

- Thick fur is used by animals for keeping warm in winter
- When fur grows it becomes thicker
- Therefore, some animals' fur grows thicker for staying warm in the winter

Therefore, some animals' fur grows thicker for staying warm in the winter
Growing thicker fur in the winter helps some animals to
- Keeping warm is the opposite of becoming cold 
- Thick fur is a kind of fur 
- Fur is a part of skin for keeping warm 
- If the environmental temperature is too cold then an animal in that environment may become cold 
- When fur grows it becomes thicker 
- An animal is a kind of living thing 
- Winter has cold temperatures 
- If a living thing becomes too cold then that living thing will die