A couple has 10 children, all female. Which of the following best explains the s...

The question is asking us to choose the best explanation for a couple who has 10 female children. The options are A, B, C, and D.

Option A states that the sex determination was by the man's X chromosome, and this is the correct answer. In humans, sex is determined by the combination of sex chromosomes received from both parents. Females have two X chromosomes, while males have one X and one Y chromosome. If the father's sperm carries an X chromosome, then the child will be female.

Option B states that the man's sperm count is low, but this has nothing to do with the sex of the children. Sperm count only affects the likelihood of conception.

Option C states that the woman is not capable of producing male children, but this is not biologically possible. The sex of the child is determined by the father's sperm.

Option D states that the sex determination was by the man's Y chromosome, but this is incorrect. As mentioned earlier, if the father's sperm carries an X chromosome, then the child will be female.

In summary, the correct answer is A, which explains that the sex determination was by the man's X chromosome. This means that the father's sperm carried an X chromosome, resulting in the birth of 10 female children.