Final answer:
If planet A is twice as far from the Sun as planet B, the period of its orbit will roughly be 4 times as long, according to Kepler's Third Law.
Step-by-step explanation:
If planet A is twice as far from the Sun as planet B, then the period of its orbit will be longer due to Kepler's Third Law, which states that the square of the orbital period of a planet is proportional to the cube of the semi-major axis of its orbit. Specifically, if the distance is doubled, the orbital period will increase by a factor of 23/2 (the cube root of 2 squared), which is approximately 2.83. Therefore, none of the given options (a. 1/2, b. 1, c. 2, d. 4) are exactly correct, but the closest answer by estimation is (d) 4 times as long.