Answer
See the explanation
Work Step by Step
a. The method ww is shown as being called on self: X in the sequence diagram. This means that the class X contains the method named ww.
b. The method xx is called on the object :Y in the sequence diagram. Therefore, the class Y contains the method named xx.
c. Based on the diagram, there is no direct arrow or message shown between :Z and :Y. All communication appears to go through self: X. Therefore, the object of type Z does not communicate directly with the object of type Y during the sequence.
