The advantages of hysterectomy in molar pregnancy are:
Hysterectomy when performed in molar pregnancy significantly decreases the chances of developing choriocarcinoma (by 5 fold times) but does not make it nil and hence follow up is required (so both options a and b are incorrect)

This is supported by following lines from Dutta-
“It should be remembered that following hysterectomy, persistent GTD is observed in 3–5% cases. As such, it does not eliminate the necessity of follow up.The enlarged ovaries (theca lutein cysts) found during operation should be left undisturbed as they will regress following removal of mole. But, if complication arises, like torsion, rupture or infarction, they should be removed.”
Dutta 7/e, p 195
Thus from above lines it is also clear that ovaries even if they are enlarged should not be removed during hysterectomy for h mole.
As far as pulmonary embolisation in concerned -acute pulmonary insufficiency due to pulmonary embolization of trophoblastic cells, is a complication seen with suction evaculation and not hysterectomy.
Chance of choriocarcinoma becomes nil
Follow up is not required
Enlarged ovaries can be removed during operation
Chance of pulmonary embolisation is minimal