Mark 13:3

New English Translation

³So^[a] while he was sitting on the Mount of Olives opposite the temple, Peter, James, John,^[b] and Andrew asked him privately,

Mark 13:3 tn Here καί (kai) has been translated as “so” to indicate the implied result of previous action(s) in the narrative.
Mark 13:3 tn Grk “and James and John,” but καί (kai) has not been translated since English normally uses a coordinating conjunction only between the last two elements in a series of three or more.

New English Translation (NET)