In a parliamentary republic, a often serves as both head of state and head of government.
a.
prime minister
b.
king
c.
dictator
d.
monarch

In a parliamentary republic, a A. Prime Minister often serves as both head of state and head of government.

Explanation: The Prime Minister is the head of the state/cabinet and leads all of the ministers who serve on the executive branch of the government. A Prime Minister often works more closely and with the overall government of the country and not just the state level 

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explanation:

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the density would be a smaller number.