Let's first assess the stimulus carefully. It presents an argument; the conclusion is "there must be more ambidextrous people who were born to women over 40 than there are ambidextrous people who were born to younger women."
What is the support provided for this conclusion? (1) A birth is more likely to be difficult when the mother is over the age of 40 than when she is younger, (2) Regardless of mother's age, a person whose birth is difficult is more likely to be ambidextrous than is a person whose birth was not difficult (3) Other causes of ambidexterity are not related to the mother's age
What is the problem? The conclusion talks about absolute numbers ("there are more people"), but the premises only tell you about proportion ("more likely," i.e., 51% of the time or more).
Answer choice (B) identifies the correct problem with this argument: "it overlooks the possibility that fewer children are born to women over 40 than to women under 40." Just because the likelihood of ambidexterity may be greater for children born to women who are over 40 does not mean that the absolute number of such children is greater, because most women have children before they reach the age of 40.
Answer choice (E) is entirely irrelevant to the conclusion. The "why" is not the issue here. You are told that birth difficulties do result in a higher likelihood of ambidexterity. OK, take that premise as given. The issue is whether that premise, and the others given, actually support the conclusion reached. They do not, for the reasons explained above.
Hope this helps. Remember: focus intently on the conclusion, the premise(s), and the links between the two. That will help you get to the right answer on logical reasoning questions. Let us know if you have additional questions!
