The euro is on course to stay below parity with the US dollar for some time if gas prices do not fall markedly, a top Wall Street bank has said. The currency used by the 19 countries that make up the eurozone is set to drop to $0.94, according to Goldman Sachs. The euro last week closed a shade below parity with the greenback. However, Goldman, in a note to clients over the weekend, predicted the currency could stay there for years if gas prices solidify above their historically low levels. “The euro area’s deteriorating external balance…