Final answer:
The author believes ratings systems do not effectively account for individual children's maturity levels, arguing that these decisions are best made by parents on a case-by-case basis. Thus, the option c is the correct answer.
Step-by-step explanation:
When the author says ratings systems are "based on numbers", she is developing the point that some decisions should be made on a case-by-case basis. Ratings systems like those implemented by the Motion Picture Association of America (MPAA) and the Entertainment Software Rating Board (ESRB) rely on quantifiable content such as instances of violence, language, and adult themes to categorize movies and video games. However, the author argues that this numerical approach doesn't account for the individual maturity and sensitivity of her children to such content. She believes parents know their children best and are more qualified to judge what is appropriate for them to watch.
The author's experience suggests that not every child of a certain age will find the content deemed suitable by these ratings systems appropriate. For example, a mature 9-year-old might handle a movie rated PG or PG-13 just fine, while even a 16-year-old might not be ready for "frivolous violence". This underscores the author's perspective that parenting decisions about media consumption should not be solely guided by the movie rating but rather tailor-fit to each child's capacity and understanding.