Today I flew into KBFI (Boeing field) which is class D and has
extentions that underlie the Class B that require close attention to
altitudes and headings so as to stay clear. Today the winds were
favoring 31L (and 31R) and I came in from the west on the Vashon
approach--the most common approach from the west.

I was on a left downwind for 31L and the tower told me I was number
three following an Arrow on about a 2 mile straight in final (Valley
approach?). I acknowledged the traffic, and was waiting for it to come
up on my 9 o'clock before turning base so as to allow enough spacing.

The controller suddenly told me that I was too far south and said
either that I had busted into surface B or was about to. (I never did
clearly hear which).
Unless one turns a fairly close in base here--within about a half mile
or less--you end up in class B surface.

My questions:

1.Assuming I busted B; who is reponsible if the controller asks me to
follow an aircraft that is too far out on a straight in? I mean, I can
reduce speed, s-turn, and the like but I can't turn base until the
aircraft on final is a safe distance away, right?

2.Is the controller supposed to arrange things so that I *can* turn
base and not be in conflict with other aircraft?

3.How would you resolve the problem if it were happening to you ?

Any thoughts would be appreciated...

Antonio