What is the principle that states the size of a just noticeable difference is a constant proportion of the size of the initial stimulus

A)  Thorndike's law 
B)  Titchener's law 
C)  Fechner's law 
D)  Weber's law

Weber's Law

A principle of perception that states the smallest change in a stimulus that can be detected is a constant proportion of the stimulus level.

Fechner's Law

A principle in psychophysics stating that the perceived intensity of a stimulus changes proportionally to the logarithm of the actual stimulus intensity.

Thorndike's Law

A principle stating that behaviors followed by positive outcomes are more likely to be repeated, whereas behaviors followed by negative outcomes are less likely to be repeated.