Answer:
The correct option is C .
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
 is the type of function 
 , where k and a are any real number,
, where k and a are any real number,
Which is the general form of a power function,
⇒ 
 is not a logarithmic function.
 is not a logarithmic function.
 is the type of function
 is the type of function 

Which is the general form of exponential function,
⇒ 
 is not a logarithmic function,
 is not a logarithmic function,
Hence, only the function in option C has written in the form of 
 .
.
Option C is correct.