makes a system easier to maintain

is often a result of high cohesion

makes a system difficult to understand

allows modules to be easily reused

shows alternative paths where one of the options will be done

is a portion of an interaction path that may be done

shows that the methods in the frame must be run in parallel

represents a repeating loop of functionality

depicts the objects involved in a scenario and the sequence of messages exchanged between the objects needed to carry out the functionality of the scenario

is a type of interaction diagram

All the options 

shows object interactions arranged in time sequence