kovarex: I'm sceptical about D5 being correct, while C5 incorrect.
The explanation is, that C5 leaves 2 go threats, but D5 seems leave even more ko threats trying to live.
Ivan Detkov: IMHO, this is not about ko-threats but a loss of a 2 or 3 points vs. strength (good aji). In many cases strength is more important. C5 is a good alternative.
I'm sceptical about D5 being correct, while C5 incorrect. The explanation is, that C5 leaves 2 go threats, but D5 seems leave even more ko threats trying to live.