3-5 point low approach one-space low pincer, kosumi, nobi
is a common response with a variety of responses. Any of a-e, as well as tenuki, are all fair game.
happens very infrequently in pro games. The circled stones are treated lightly.
Here is one of the few pro games where this happens.
Black player: Gu Li
Black rank: 7p
White player: Ding Wei
White rank: 8p
Event: Tianyuan, 17th
Place: Beijin, China
Round: Quaterfinal - 2
Game time: 3 hours
Board size: 19
Number of moves: 207
To my 8-kyu eyes, the sacrifice of those four stones isn't something to be taken so lightly (no pun intended). But Black ended up winning the game, so what do I know? :P