Your layout has four floated elements in a row but unfortunately the last element has wrapped to a fiew line. What is the source of the layout mistake?

a$.$ The widths of the floated elements exceed the available width of their container.

b$.$ You cannot float more than one object within a row.

c$.$ You have to clear the first three floating object to make room for the fourth.

d$.$ You have to clear the fourth floating object to make room for the first three.