A parasite is a living organism that lives inside or outside of another organism called a HOST in order to obtain nourishment from such organism. A parasite that lives inside its host is called ENDOPARASITE while a parasite that lives outside its host is called ECTOPARASITE.
In this question, a worm that lives inside a bear is a PARASITE because it is living inside the bear, which is the host in order to obtain nourishments. Note that, the answer is not option D because the bear is a HOST not a parasite.
The bouyant force is the capabilty that an object has of floating. Only things that are less dense than water can float on it.
When you bring water inside the submerged submarine nothing happens since the bouyant force only applies to things that float on the fluid we're taliking about.
