A Researcher Wants to Study the Effects of Head Injury

A researcher wants to study the effects of head injury in children under the age of 5 years on mothers' decisions to work outside of the home.Which of the following factors negatively affects the feasibility of this study?

A) The local region has a high percentage of single-parent families.
B) Head injuries in children under age 5 represented less than 1% of hospital admissions during the year previous to the study.
C) Children under the age of 5 years are not able to read, write, or give direct informed consent to participate in this study.
D) A comprehensive review of the literature shows no studies that examined this question were conducted during the past 15 years.