If there is an oil-supply disruption resulting in higher international

Argument:
If intl oil prices rise, domestic oil prices for open-market countries will rise too, whether such countries import all or none of their oil

So even if a country does not buy its oil from intl market, its price will move up with intl prices.

We need an option that is the conclusion i.e. it is supported by the argument.

(A) Domestic producers of oil in open-market countries are excluded from the international oil market when there is a disruption in the international oil supply.

No. Our argument is instead implying that domestic producers are linked to intl market.

(B) International oil-supply disruptions have little, if any, effect on the price of domestic oil as long as an open-market country has domestic supplies capable of meeting domestic demand.

Incorrect. Again, the argument is saying that intl oil supply has effect on domestic prices.

(C) The oil market in an open-market country is actually part of the international oil market, even if most of that country’s domestic oil is usually sold to consumers within its borders.

Correct. The argument is telling us that domestic oil market is a part of intl market and moves with it. This is the best option, though it may not be perfect. The argument talks about "even when there are no imports". This option talks about "even when there are no exports". Still, the gist is the same - that domestic market moves with intl market.

(D) Open-market countries that export little or none of their oil can maintain stable domestic oil prices even when international oil prices rise sharply.

Not correct. Our argument says that domestic market moves with the intl market. So we cannot conclude that domestic markets can maintain stable domestic oil prices when international oil prices rise sharply. At best, we don't know what happens with domestic prices when the country does not export and intl prices rise. What we know is that even if the country does not import, the domestic prices move with intl prices.

(E) If international oil prices rise, domestic distributors of oil in open-market countries will begin to import more oil than they export.

We cannot conclude this. We do not know what domestic distributors will do.

Answer (C)­