Answer
There are three elements of unsaturation in Limonene. It can be concluded that two elements of saturation were lost and one is left in the molecule.
Work Step by Step
There are three elements of unsaturation. Since the reagent $H_2/Pt$ only reduces two elements of unsaturation (there are 4 more H), there are two double bonds or one triple bond. So the third element of unsaturation must be a ring.