1993 年

In the figure, $ABCD$ and $EFGH$ are two squares and $ACH$ is an equilateral triangle. Find $AB:EF$.

In the figure, a rectangular piece of paper $ABCD$ is folded along $EF$ so that $C$ and $A$ coincide. If $AB=12\text{ cm}$ and $BC=16\text{ cm}$, find $BE$.

In the figure, the three circles touch one another. $XY$ is their common tangent. The two larger circles are equal. If the radius of the smaller circle is $4\text{ cm}$, find the radii of the larger circles.