Answer:
C: A randomized block design experiment
Explanation:
We are told the participants are divided by gender into groups which we can call blocks. Then, within each group, they are randomly assigned to either the treatment or control group. This means they are assigned treatments within each block.
A randomized block design is defined as an experimental design whereby the experimental units are divided into groups which we call blocks. After that treatments will be randomly assigned to the experimental units within each of the blocks.
Thus, this corresponds with our question and we can say it's a randomized block design experiment.