The correct options are
A They are acidic in nature.
D They react with base to form salt and water.
Reaction of non-metal oxide with base is:
Non-metal oxide + Base→Salt + Water
An example of the above reaction is:
CO2 is a non-metal oxide and Ca(OH)2 is a base. They react to form CaCO3 (salt) and water.
Comparing it with neutralisation reaction where acid reacts with base to form salt and water, we can conclude non-metal oxides are acidic in nature.