All on 1 layer

Exports all contours onto one AutoCAD layer

Separate layers

Exports onto separate layers having the layer name the same as the contour level.

Contour lines

Export the lines only

Contour bands

Export the contour bands.  Also enables Contour bands export options

3DFace

Export bands as 3Dfaces

Polyline + Hatch

Export the bands as a hatch object

Solid

Default setting export as solid objet