Jamieson, Fausset and Brown on Mark 13:3

3. And as he sat upon the Mount of Olives, over against the temple--On their way from Jerusalem to Bethany they would cross Mount Olivet; on its summit He seats Himself, over against the temple, having the city all spread out under His eye. How graphically is this set before us by our Evangelist!

Peter and James and John and Andrew asked him privately--The other Evangelists tell us merely that "the disciples" did so. But Mark not only says that it was four of them, but names them; and they were the first quarternion of the Twelve.