Answer
See explanation below.
Work Step by Step
The market share is a fraction, often expressed as a percentage, but it cannot exceed $1=100\%.$ (Owning $ 120\%$ of the market makes no sense.)
A function of the form $y=A\log_{b}t+C$
with positive coefficients A and C is an always rising function, and it will eventually EXCEED the value of $100\%.$
So, in the long term, it will not be appropriate for representing the market share.
