English Language · Vocabulary Replacement

In the question given below, a sentence is given with three words highlighted in bold. Three replacement sets are provided. Select the option that gives the correct combination of options that can replace the bold words logically and grammatically. 'Environmentalists who examine migratory patterns have reached the conclusion of suggesting that the sudden population shift was a singular event unlikely to be witnessed again.' 1. observe, asserting, possibly2. monitor, maintaining, impossible3. study, hypothesizing, improbable