Unitary states are the states that have a central government which has all the administrative powers (in contrast to a confederation, union etc.).
a) WRONG We have that a dictatorship or a monarchy in a state still qualifies it as a unitary state.
b) WRONG The majority of the states in the worlds are unitary and there are many outside Asia (France, UK etc.).
c) They are not divided in many autonomous regions; that would be a characteristic of a federation. They can be divided in regions that have some powers but are ultimately subject to the central government.
d) The majority of the states have always been unitary, so no increase was observed.
The correct answer is E since this makes the state more homogeneous and there are less differences to account for over the whole territory. For example, a country that has both sea and mountain tourism would be harder to become regulated in that respect than a small sea-side country.