I think ABC is correct.
Skinny tables can contain a maximum of 100 columns. It's a feature of skinny table. But it does not make skinny table fast than others options do.

A,C,E
Although skinny tables are kept in sync: https://developer.salesforce.com/docs/atlas.en-us.salesforce_large_data_volumes_bp.meta/salesforce_large_data_volumes_bp/ldv_deployments_infrastructure_skinny_tables.htm
I do not see how this speeds up things. Limiting number of columns sounds more logical.

Skinny Tables are not kept in synch with Custom object schema changes.
If a custom object Field which is included in skinny table and its type is changed then the skinny table becomes "obselete".
Skinny Table is fast bcoz they avoid intensive joins, they don't inlcude soft-deleted records & at max they can support 100 fields (select field with appropiate care...)