At which study visits can the sponsor expect to review subjects' signed informed consent forms?

The correct answer identifies that the sponsor can expect to review subjects' signed informed consent forms during periodic and termination site visits.

During periodic visits, the sponsor is actively monitoring the study's progress and ensuring compliance with regulatory requirements and the study protocol. This includes verifying that participants have provided informed consent before any study-related procedures commence. Reviewing signed consent forms at these visits helps to ensure that ethical standards are upheld and that participants have received all necessary information regarding the study, its risks, and benefits.

At termination site visits, when the study concludes, it's crucial for the sponsor to review these forms to ensure all participants had properly consented and to confirm that procedures for consent were followed throughout the trial. This is important not only for ethical reasons but also for maintaining proper documentation that might be required during audits or inspections.

The other choices may have elements of oversight, but they do not fully encompass the comprehensive checks for signed consent forms during the most critical periods of active monitoring and study closure as outlined in the correct answer.