The correct answer is C. Review.

A review is an activity that includes confirming understanding, brainstorming, and testing ideas. It is a formal process of evaluating a product, service, or process to ensure that it meets the requirements of the stakeholders. Reviews can be conducted at any stage of the development process, from the initial concept to the final product.

Brainstorming is a technique used to generate creative ideas. It involves bringing together a group of people to share their ideas in a free and open environment. Brainstorming is often used in reviews to generate new ideas for improving a product or service.

Testing is the process of evaluating a product or service to ensure that it meets the requirements of the users. Testing can be conducted manually or automatically. In reviews, testing is often used to verify that the product or service meets the requirements of the stakeholders.

Code walkthrough is a technique used to review code. It involves walking through the code line by line with a group of people to ensure that the code is clear, concise, and easy to understand. Code walkthroughs are often used in reviews to ensure that the code is of high quality.

Inspection is a technique used to review documents. It involves reviewing the documents line by line with a group of people to ensure that the documents are accurate, complete, and up-to-date. Inspections are often used in reviews to ensure that the documents are of high quality.

Therefore, the only option that includes confirming understanding, brainstorming, and testing ideas is C. Review.