Jessica was born long before her due date, and was significantly underweight at birth. This was most likely because her mother smoked cigarettes during the embryo stage of her pregnancy as she was not smoking cigarettes during the fetal stage of her pregnancy and the zygote stage carries with it the least amount of risk from cigarette smoking. Fortunately, Jessica was an incredibly resilient infant, and easily caught up with her age-mates in most developmental areas. By age two, Jessica’ s language skills were on par, and she was uttering short sentences, such as "want juice." She regularly engaged in make-believe play with her favorite stuffed animals and loved using crayons to draw pictures of the people in her family, including her dog, Skippy. By age seven, Jessica absolutely loved school because she had an insatiable desire to learn and become good at all of the interesting academic subjects she had previously heard about, including math, history, and art. She derived a ton of pleasure from the tasks her teacher assigned in school, and because she started to excel above many of her peers, she felt very good about herself. When Jessica was in 5th grade, a scientist named Dr.Chavez visited her classroom to discuss a 2-week study that he was conducting, examining the similarities and differences among themes represented in artistic drawings among children of ages 5, 10, and 15. Since Jessica loved to draw, she hoped her mother would allow her to participate in this study.

Dr. Chavez’s 2-week study examining the similarities and differences among themes represented in artistic drawings among children of ages 5,10, and 15 is an example of ____ research.
a. Longitudinal
b. Ethnographic
c. Case study
d. Cross-sectional