- The testes is a source of male gametes in animals
- A source of something produces that something
- Hence, the testes produce male gametes in animals

- The testes produce male gametes in animals
- A human is a kind of animal
- So, the testes produce male gametes in humans

So, the testes produce male gametes in humans
Question
Which of these structures produces male gametes in humans?

Context
- The testes is a source of male gametes in animals 
- A source of something produces that something 
- A human is a kind of animal