Which one of the following is a parasitic algae?

The correct option is A Cephaleuros
Cephaleuros is a genus of parasitic thalloid algae comprising approximately 14 species. Its common name is red rust. Specimens can reach around 10 mm in size. Dichotomous branches are formed. The alga is parasitic on some important economic plants of the tropics and subtropics such as tea, coffee, mango and guava causing damage limited to the area of algal growth on leaves (algal leaf spot), or killing new shoots or disfiguring fruit. Members of the genera may also grow with a fungus to form a lichen that does not damage the plants