Three species of frogs—lithobates pipiens, lithobates clamitans, and lithobates sylvatica—all mate in the same ponds, but they pair off correctly because they have different calls. this is a specific example of a barrier, called

"This is a specific example of a reproductive barrier, called behavioral isolation or sexual isolation".

Explanation:

Reproductive barriers are isolation mechanisms that prevent mating between two or more species. The prezygotic mechanism avoids fertilization between individuals of different species, and the postzygotic mechanism avoids the zygote to develop and reach the adult stage.

There are different types of reproductive barriers, one of them is behavioral isolation, also known as ethological isolation or sexual isolation. This is a prezygotic barrier that refers to the fact that many species occupy the same area but they are not sexually attracted to each other and might even be rejected because of behavioral factors, and this is why they do not get to mate. This mechanism includes courtship patterns or mating rituals, and specific chemical signals that allow the recognition between individuals of the same species. A typical example is the recognition songs of some species like frogs, birds, insects, and etcetera.

"d.) carbon dioxide and hydrogen sulfide"