SDM: Usecase diagrams

Quick questions

Q1 A usecase represents:
A role that may be played by a user of the system
A role that may be played by something outside the system boundary that may interact with the system
A coherent unit of functionality that the system should support
A class in the system
A subsystem

Q2 An actor represents:
A role that may be played by a user of the system
A role that may be played by something outside the system boundary that may interact with the system
A coherent unit of functionality that the system should support
A class in the system
A subsystem

Q3 The line between an actor and a use case is:
A link
An association
A string
A generalization

Q4 There can be instances of (tick any that apply):
A usecase
An actor
A [whatever you said that line between an actor and a usecase is]