Teire/Solution2

Uh-oh  

at . After , Black should play at and give up four stones. If Black resists all the way, the result is much worse.

 

Any of these three work equally well. I have a minor preference for the top one. -Joshua

Malcolm : Black has 7 different ways of protecting. I agree with Joshua that 'a' is perhaps the best as it makes strong eye shape, and only leaves one ko threat.