In which sentence is the underlined phrase an adjective clause? a male platypus can eject venom when another animal disturbs it. the platypus, which is a mammal, has a bill like a duck and feet like an otter. when explorers first sketched the platypus, scientists thought the sketches were a hoax.

The platypus, which is a mammal, has a bill like a duck and feet like an otter is the right answer

The correct option is A.
In the passage given above, sentence 1 and 2 introduced the main idea of the passage while sentence 3 to 6 serve to add supporting details to the main idea that has been introduces. The sentences throws more light on the physical description of the cottage.