Answer:
A. Species.
Explanation:
A species is classified as being able to interbreed together. In this case, a human boy and a human girl can interbreed.
Offspring does not make as much sense in this case, for there is no context to allow it to be the correct answer. Boys and girls are technically terms used for kids, which equate to offspring, however it is not your answer.
Boys and girls also are not the same gender. They equate to the norm of gender binary, which means that there are two genders, being male (boy) and female (girl). As by definition, this is not malleable, and individuals fit into one or the other typically based on natural development.
Therefore, Species is the only satisfactory answer in this case.
