 Solution

A sequence diagram describes an interaction among participants using lifelines and ordered messages; time normally runs downward. Calls, replies, and execution intervals show a scenario such as the client asking a Sports wrapper for its cost, then that wrapper delegating through the inner packages to BasicPlan and adding charges on return. Alternatives or loops can describe more than one trace.

A state diagram describes states of an object or system and transitions triggered by events, possibly guarded by conditions and accompanied by actions. An account might move from active to suspended on a failed-payment event and back to active on payment. It describes allowed lifecycle behavior rather than the order of messages in one chosen interaction. Both are behavioral diagrams in UML.