Cynthia is interested in the effects of learning outcomes of questions within instructional materials delivered to learners via the web

Cynthia is interested in the effects of learning outcomes of questions within instructional materials delivered to learners via the web. She randomly assigns students to groups given either material with questions or materials with no questions and assesses the effects of the question based upon student performance on multiple-choice questions administered after learning. of the following Cynthia's research could best be described as

a. Survey

b. Correlational

c. Experimental

d. Historical