Betty and Veronica, the Central Park Zoo’s newest inhabitants make their official debut today.  They’ve been busy  exploring all the nooks and crannies of their new home, a radically redesigned enclosure that once housed Gus, the Zoo’s beloved polar bear who died in 2013.  Visitors who were accustomed to Gus’s endless lap swimming — the aquatic equivalent of pacing — are in for a treat. These bears are social, engaged and, considering that it’s winter, pretty active, in a lumbering sort of way.