Mario Is a STEM Researcher Who Wants to Test If

Mario is a STEM researcher who wants to test if field-based experiences in high school lead to increased long term engagement in STEM fields. He first measures students' attitudes toward STEM careers in the beginning of their junior year of high school. Then, students are randomly assigned to one of three conditions. Students in the first condition are assigned to no field-based experiences, the second condition provides one three-week experience, and the third condition provides two different three-week experiences. He not only measures attitudes at the end of the academic year but tracks students for three years to test attitudes again one year and three years after the treatment to examine if any effects.
-How many levels of the independent variable are represented in Mario's study?

A) 1
B) 2
C) 3
D) 4