What element could x represent

What is the missing step in this proof? scroll down to see the entire proof. u

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The graph shows the populations of two species in a particular region over two decades. based on the graph, what can you conclude about the relationship between the two species? a. the two species have a parasitic relationship. b. the two species are mutualistic in nature. c. the two species exhibit commensalism. d. the two species have a prey-predator relationship. e. the two species have a familial relationship.