Question 193
Telephone exchange extensions have only 2 digits, from $00$ to $99$. Not all extensions are in use. Changing the order of two digits of an extension in use, you either get the same number or a number of an extension that is not in use. The largest possible number of extensions in use are:
(A) Less than $45$
(B) $45$
(C) between $45$ and $55$
(D) more than $55$
(E) $55$
(A) Less than $45$
(B) $45$
(C) between $45$ and $55$
(D) more than $55$
(E) $55$