Answer:
The correct answer is -
19 - C) parasitism
20- B) commensalism
Step-by-step explanation:
Parasitism is a type of symbiotic relationship among two different organisms where one is benefited and the other is harmed. The harmed organism known as the host and the benefitted organism called the parasite. For instance, tapeworms are parasites in the human body.
Commensalism is also a symbiotic relationship but in this relationship, one symbiont is benefitted but another one neither benefitted nor harmed. For instance, Hermit crabs use the shells of dead snails for homes.