Answer is B

According to the Salesforce documentation(1), the answer is:

B - Reset the DOM after each test with the afterEach method.

The afterEach method is a Jest function that runs after each test in a describe block. You can use it to perform any cleanup tasks that are needed after each test, such as resetting the DOM, clearing mocks, or restoring spies. In your case, you can use the afterEach method to reset the DOM to its original state after each test, so that the next test can start with a clean slate and avoid any interference from the previous test’s DOM manipulations.

The other options are not correct. You do not need to add a teardown block to reset the DOM after each test, as this is a Jasmine feature that is not supported by Jest. You do not need to create a new describe block for each test, as this would create unnecessary nesting and duplication of code. You can use multiple tests within the same describe block to test different scenarios of your component. You do not need to create a new jsdom instance for each test, as this is done automatically by Jest when you import @salesforce / sfdx-lwc-jest / config in your jest.config.js file.

https://developer.salesforce.com/docs/platform/lwc/guide/testing.html...