Please the paragraph below and answer the questions:

"Joanna was a researcher who conducted quasi-experimental research studies. She was interested in the effectiveness of a tutoring program on fifth-grade students' math performance. She conducted a study on two groups of fifth-grade students. Joanna administered a new tutoring program to one group and did not administer a new tutoring program to the other group. Results showed that the students exposed to a new tutoring program had higher grades than the students not exposed to the new tutoring program."

What is the design that Joanna used in her study? (e.g., non-equivalent, one group pretest-posttest design, combined method)

What are the potential threats to the internal validity of the experiment? List and explain each