A1 is the best, because it relates most closely to the question. As you know, we can use the definite article + singular noun to refer to a species as a whole - for example 'The elephant is the world's largest land animal'. If the question were 'What are your favourite animals? , then A4 would be the best answer. If you were looking at a picture of different animals, and someone asked you 'Which are your favourite animals?', then you'd answer A2. This would refer to the specific kangaroos in the picture. I can't think of a situation where A3 would be an appropriate answer.

Thank you for your selection

A1