Bitcoin’s more-than 20 percent slump this week on China’s reported plans to shut down cryptocurrency exchange trading has investors speculating when it will drop below the key psychological level of $3,000. But the level to watch may be just beyond that threshold: $2,877. Not only is that bitcoin’s intraday high on Aug. 4 — about the time the digital currency’s most recent leg up began — it’s also bitcoin’s current 100-day moving average. For Chris Weston, IG Ltd.’s chief market strategist in Melbourne, $2,877 is a “key line in the sand” and “the bulls will want to see this hold,” he said.