Where does a line box ends?

Question:

Let's say we have a right floating element just at the end of a something that results to be the end of a secuence of line boxes (in a inline formtt. ctx). Must it be:

a) rendered vertically lined with top of last line if horizontally fits without exceding container dimensions or...
b) always rendered vertically lined with bottom of last line box 

In: http://www.w3.org/TR/CSS21/visuren.html#img-flow-clear seems that answer is a)