The correct answer is option 2- plungedFrom the context, it is clear that we have to find out the reaction of the stock market to the news of the coup. A stock market can rise, fall or remain stable. Plunged: fell suddenly and uncontrollably; suffered a rapid decrease in valueThus 'plunged' fits the blank both grammatically and contextually. The meaning of the other words-Poised: been or caused to be balanced or suspendedPlugged: blocked or filled in (a hole or cavity)Probed: physically explored or examined (something) with the hands or an instrument