The Flow Switch activity is a conditional node that provides branching for the flow of control based on a match criterion when more than two alternative branches are required. The Flow Switch activity has an Expression property that can be of any type, and a dictionary of Cases that consists of pairs of keys and activities. The Flow Switch activity evaluates the Expression and compares it against each of the keys in the Cases. If a match is found, the corresponding activity is executed. If no match is found, the Default case is executed, if it is defined. The Default case is an optional activity that serves as a fallback option when none of the cases match the expression. Therefore, the answer is D. Default case is executed if no cases match the expression. References: Flow Switch, About Control Flow