I believe that the only two options are b or d. My initial gut feeling was that d was the correct move, because it split the white side, and if ignored left potential to be exploited.
However, at second glance, b looks better, as it puts some pressure on the white group on the lower right side and extends from the IkkenTobi in the top right.
Yet, white could still simply extend down and then potentially get an eye to start running with. However, that running might help black build up a moyo on the top too much.
What is the appropriate way to engage white?
Jasonred Hmmm, I'm guessing that b is best, cause "it is too big to be ignored" and a defence of it will at the least, I'm guessing, end up with a nice group for black to expand and cause chaos with, possibly a wall there if your opponent is bent on keeping the corner... I also saw the hint about your opponent's move, and I thought, well, hey, you really need TWO points to enclose a corner, and he's only got one, right?
Gilles b is obviously the best point. It is an extension (vital in my opinion) for both sides.
However, the situation looks a bit artificial. The marked white stones should be followed by b. If W didn't play b, she should not have played this marked stone. This should be confirm by a stronger player...
Spectrums- I like a or c on this one. Nothing has been developed on the side, and no matter what white does, you can still grab a piece of the center.
griffin- B is by far the best in my opinion. A extends to the secondary direction of the encloure, but why when you can extend to the primary? The marked black stone is low, thus that whole side is disvalued. since extending from an enclosure and to one have the same value, and since the marked stone is low whereas the white stones below B have potential to be attacked, B is better. D is certainly a good point,but "urgent before big". White has neglected to make a base, and B punishes white for that omission, plus is and ideal extension. B also serves 2 purposes, while D only serves one.
Move on to: Fuseki Exercise 2