Final answer:
Great Danes and Chihuahuas are of the same species because they are genetically compatible and can interbreed despite their size and appearance differences. This is due to their similar genetic make-up and shared ancestry, which allows for successful reproduction.
Thus option a and c is correct answer.
Step-by-step explanation:
Great Danes and Chihuahuas are considered members of the same species primarily due to their genetic compatibility and their ability to interbreed. These are key characteristic factors that define a species. Despite their drastic differences in size and appearance, which might not make them look like they have similar physical characteristics, these two dog breeds can produce fertile offspring thus highlighting their close genetic relationship. While they do not share a shared habitat naturally, it is not a defining feature of a species.
Members of the same species share a high level of DNA alignment, which means they have similar genetic make-up that leads to successful reproduction. Through the process of artificial selection, humans have managed to create a wide variety of dog breeds from the same ancestor, which are genetically almost identical.
This is a demonstration of homology, where different species share characteristics due to a common ancestor, much like the structural similarities visible across various species of vertebrates.
Thus option a and c is correct answer.