And f(-32a)=34a when the straight line y=kx+t coincides with AB,

∴f(32a)=f(-32a)，

Also, the regular hexagon ABCDEF is both a centrally symmetric figure and an axisymmetric figure.

The function S=f(t) is an even function.

So choose a.

Method 2: compare f(t) and f(-t): when it is t, the straight line is y = kx+t, when it is -t, the straight line is y = kx-t, and the triangle is OM'N'. These two lines have opposite intercepts and the same slope. They are symmetrical about the center of the origin. Hexagons are also symmetrical about the origin. Then the straight line is symmetrical about the center of the origin.

So it is an even function.

So choose a.