Which of the following statements about systems and feedback are true? (select all that apply)
a) Both positive and negative feedback can lead to system instability and collapse.
b) A system is essentially a network, with materials and energy flowing from one component to another.
c) With positive feedback, an increase in a state variable leads to further increases in that same variable.
d) With negative feedback, an increase in a state variable leads to further increases in that same variable.
e) All systems are closed.
