It is defining.
Defining relative clause does not have a comma, while a non-defining relative clause has.
For example, if the sentence is:
The children, who hate chocolates, are uncommon.
- since there is comma in this sentence, it is non-defining.
- while if there is no comma like the question in the picture, it is defining.
Answer:
The testing effect shows that learning and memory are enhanced by actively retrieving, rather than simply rereading, previously studied material.
Explanation:
Hmm, I would probably go with B. While both I think are correct, B makes a little more sense.
