Here’s a possible completion of the passage using the words provided:

Brunei is one of the (16) **smallest** countries in the world. Its population is only 25,000 and (17) **most** of them live in the capital city. It is also the richest country in Asia and may be the richest country in the world because it has a lot of oil and (18) **natural** gas which it exports to Japan. Every week huge tankers carry oil and gas from the oil-fields of Brunei to Japan. The head of the state in Brunei is Sultan Haji Hassanal Bolkiah. He is the richest man in the world. He has two wives and each lives in their own beautiful palace. The first wife lives in the biggest palace in the world which has 200 (19) **rooms**. The Sultan has more than 200 cars and he also has hundreds of (20) **horses**.