Answer:
The correct option is C .
Step-by-step explanation:
A logarithm function is written in the form of
,
Since, y = 0.25x is the type of function y = mx + c,
Which is the general form of a linear function,
⇒ y = 0.25x is not a logarithm function,
is the type of function
, where k and a are any real number,
Which is the general form of a power function,
⇒
is not a logarithmic function.
is the type of function 
Which is the general form of exponential function,
⇒
is not a logarithmic function,
Hence, only the function in option C has written in the form of
.
Option C is correct.