A partial parasite is the one which

A partial parasite is the one which absorbs water and mineral salts from the host.

They are called partial parasites because they are dependent on the host plants only for water and mineral salts, not for sugars or food.

Partial parasites do not need food from hosts because usually they are chlorophyllous and can photosynthesise.

Hence option A: Absorbs water and mineral salts from the host is the correct answer.