Which best describes a unitary system?

a. An arrangement in which the central government has authority over all lower levels of government, and those lower levels have no powers reserved for them
b. A system with an economy is modern enough to require leaders to work closely with a large bureaucracy with expertise on policy matters
c. A system in which the executive and legislative branches are controlled by the same political party
d. A system with an official ideology; a single mass political party, usually with a single leader, that has a monopoly of political power; a secret police force and the use of terror against the population; a monopoly over means of communication; a monopoly over weapons in society; and a command economy
e. A regime type defined by its rule by a single leader or small group of leaders, limited political participation, existent but limited autonomy of society from state control, the lack of an overarching ideology, and limited control over the economy

A