What if none of these amortizable asset classifications apply?

Amortization is really just depreciation for intangible assets. If the asset you're entering is a piece of equipment or something else that can be physically seen and quantified, then it's probably a tangible asset. If that's the case, go back to the previous screen and choose a different "Asset Type" or go back further and pick a different "Asset Category", then a different "Asset Type".

If you're sure this is an amortizable asset, then just choose the classification that is the closest fit.