Which of the following statements are correct regarding Kingdom Protista?
(a) Cell body contains a well-defined nucleus
(b) Protists reproduce asexually and sexually
(c) Many protists are planktons, while some are parasites.

Being eukaryotes, the protistan cell body contains a well-defined nucleus and other membrane bound organelles. 
Protists reproduce asexually and sexually by a process involving cell fission and zygote formation respectively.
Protists are mostly aquatic organisms, found in the sea, fresh water and moist soil. Many protists are planktons, while some are parasites.