Imagine a Hypothetical Pathway in Which Precursor X and Precursor

Imagine a hypothetical pathway in which precursor X and precursor Y are combined by enzyme Z in order to produce neurotransmitter XYZ. Which of the choices below would represent feedback inhibition?

A) Increasing levels of X or of Y lead to a reduction in activity of enzyme Z.
B) Increasing levels of enzyme Z lead to an increase in levels of XYZ.
C) Increasing levels of enzyme Z lead to a reduction in availability of X and Y.
D) Increasing levels of XYZ lead to an increase in the availability of X.
E) Increasing levels of XYZ lead to a reduction in the activity of enzyme Z.