Explanation
A partial selector is a selector that does not contain the information about the top-level window. A partial selector is usually generated when a UI Automation activity is included in a container activity, such as Attach Browser or Attach Window, that has a full selector of the outer window. This way, the UI Automation activity can use the partial selector relative to the container, instead of the full selector from the root. Therefore, the answer is B. When included in an Attach Browser activity. References: Full Versus Partial Selectors, Attach Browser