C- is the only one that works here. The sentence is referring to something that will (probably) happen after an event in the future. E- won't work because when they presented it would describe a series of events in the past, while is likely to arise describes probable events in the future.
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AnonymousA dispute is likely to arise among union members about the terms of the new contract when they________________ it for the first time.What does "they" refer to? What does "it" refer to?