Actually 'proving' that Opinion "a" is at least based on a very outdated concept when it comes to biological sex determination is pretty much a walk in the park ...
https://www.scientificamerican.com/article/sex-redefined-the-idea-of-2-sexes-is-overly-simplistic1/
"For many years, scientists believed that female development was the default programme, and that male development was actively switched on by the presence of a particular gene on the Y chromosome. In 1990, researchers made headlines when they uncovered the identity of this gene, which they called
SRY. Just by itself, this gene can switch the gonad from ovarian to testicular development. For example, XX individuals who carry a fragment of the Y chromosome that contains
SRY develop as males.
By the turn of the millennium, however, the idea of femaleness being a passive default option had been toppled by the discovery of genes that actively promote ovarian development and suppress the testicular programme—such as one called
WNT4. XY individuals with extra copies of this gene can develop atypical genitals and gonads, and a rudimentary uterus and Fallopian tubes. In 2011, researchers showed that if another key ovarian gene,
RSPO1, is not working normally, it causes XX people to develop an ovotestis—a gonad with areas of both ovarian and testicular development."
Plenty more where that came from