The role of the president has evolved over time because
a) the needs of the nation have changed.
b) the role of the executive branch has changed.
c) the role of congress has changed.
d) the needs of the chief of staff have changed.

The role of the president has evolved over time because: a) the needs of the nation have changed.

The role of the president has evolved over time because the needs of the nation have changed. Option A is correct.

The president is a common title for the head of state in most republics. In politics, president is a title given to leaders of republican states. The functions exercised by a president may se different according to the form of government.  

In authoritarian regimes, a dictator or leader of a one-party state is also recognized as a president.

i think its 5! hope i