Why did hobbes believe that the best form of government had a king as its sovereign?

 Because he felt people otherwise are too chaotic, and so to have order and stability, a strong leader is needed with full power concentrated in his hands.

Thomas Hobbes published a famous work called Leviathan in 1651.  The title "Leviathan" comes from a biblical word for a great and mighty beast.  Hobbes believed government is formed by people for the sake of their personal security and stability in society.  In Hobbes'view, once the people put a king (or other leader in power), then that leader needs to have supreme power (like a great and mighty beast).    Hobbes' view of the natural state of human beings without a government held that people are too divided and too volatile as individuals -- everyone looking out for his own interests.  So for security and stability, authority and the power of the law needs to be in the hands of a powerful ruler like a king or queen.  And so people willingly enter a "social contract" in which they live under a government that provides stability and security for society.

d is the answer. leo should include the source.