No national productivity measures are available for underground industries that may exist but remain unreported. On the other hand, at least some industries that are run entirely by self-employed industrialists are included in national productivity measures. From the information given above, it can be validly concluded that

• there are at least some industries run entirely by self-employed industrialists that are underground industries
• no industries that are run entirely by self-employed industrialists operate underground
• there are at least some industries other than those run entirely by self-employed industrialists that are underground industries
• there are at least some industries run entirely by self-employed industrialists that are not underground industries