They are the Executive, (President and about 5,000,000 workers) Legislative (Senate and House of Representatives) and Judicial (Supreme Court and lower Courts).
The answer is D
The mariner's astrolabe was an instrument originally developed by Arab astronomers for measuring the height of heavenly bodies above the horizon and came into use in navigation by about 1470.
The instrument was used to help establish the ship's latitude from the height of the Pole Star or of the sun. Sailors, at night, spotted the Pole Star through small pinholes in the the two vanes that were mounted on an alidade. This rule pivoted to allow the altitude to be read from the scale on the outer edge of the instrument.To determine the Sun's position during the day, the astrolabe was put below the waist and the alidade was set so that a beam of sunlight passed through the top pinhole onto the bottom one.
Limiting the spread of communism to new countries