The NIH Is Taking Proposals for a New Research Grant

The NIH is taking proposals for a new research grant they are bestowing. The NIH is particularly interested in research proposals that use an A-B design. Which of the follow research designs would be most appropriate for the grant?

A) Research that assesses obsessive-compulsive disorder symptoms and then requires participants to touch a public toilet seat and then reassesses obsessive-compulsive symptoms.
B) Research that requires participants to touch a public toilet seat and then assesses obsessive-compulsive symptoms.
C) Research that assesses obsessive-compulsive symptoms and then participants are required to touch a public toilet seat and their obsessive-compulsive symptoms are reassessed. Then participants are permitted to release the toilet seat and their obsessive-compulsive symptoms are assessed again.
D) Research that assesses obsessive-compulsive symptoms and requires participants to touch a public toilet seat, then reassesses obsessive-compulsive symptoms, then the participants are permitted to release the toilet seat and their obsessive-compulsive symptoms are assessed, followed by reintroduction of touching the toilet seat and assessment of obsessive-compulsive symptoms.