Answer:
The correct answer will be option D.
Step-by-step explanation:
Planets orbit around the Sun (star) due to the gravity of this star which pulls down them around it. This gravity is the vital force which maintains the elliptical path of their orbit.
If this force of gravity will change it will affect the celestial bodies revolving around it like a planet as this force of gravity is directly proportional to mass and inversely proportional to the distance between them.
According to the question if the gravity of the star increases it will change the orbital path of the planets as they will be more pulled towards the sun which will decrease the distance between the star and planet and the orbital path will become smaller and the orbital period will increase.
Thus, option D is the correct answer.