i would play b to "break" between the 2 white influence groups.
grolich: It seems to me that "a" has to be the solution. I have to restate Alex's question: is this a "solution", or an attempt? I'd be very surprised if the solution was not "a" and would like to know the source of that problem.
kb: Indeed, a is the solution. This nullifies the influence of the very thick stones.
kb: here will be met with , utilizing the wall to the left. Furthermore, White has a move like a or b to look forward to, or even c.
On to Fuseki Exercise 11.