question:  What is ironic about the Earthmen selling gas to the Zurians?
context: "It is an outrage," said Koltan of the House of Masur, "that the Earthmen land among the Thorabians!" Personally, he was in favor of the coming of the Earthmen to the world of Zur. By this, he seemed to imply that the Thorabians would rob the Earthmen, which the Lorians would not. The Earthmen were going to do great things for the whole world of Zur. Accurate reporting, much less a newspaper, was unknown on Zur. Immediately, the Earthmen established what they called "corporations"—Zurian trading companies under terrestrial control. In spite of the fact that a terrestrial ship had landed at every Zurian city of major and minor importance, and all in a single day, it took some time for the news to spread. Within five years of the first landing of the Earthmen, every major city on the globe had a printing press, a daily newspaper, and enjoyed the instantaneous transmission of news via telegraph. "As I have always said from the beginning," chortled Director Koltan, "this coming of the Earthmen had been a great thing for us, and especially for the House of Masur." Alas for that suggestion, no newspaper would accept advertising from the House of Masur; all available space was occupied by the advertisements of the Earthmen. For another, the Earthmen had procured legal authority to prospect the planet for metals, of which they found a good deal, but they told no one on Zur of this. What they did mention was the crude oil and natural gas they discovered in the underlayers of the planet's crust. Crews of Zurians, working under supervision of the Earthmen, laid pipelines from the gas and oil regions to every major and minor city on Zur. By the time ten years had passed since the landing of the first terrestrial ship, the Earthmen were conducting a brisk business in gas-fired ranges, furnaces and heaters ... and the Masur stove business was gone. Moreover, the Earthmen sold the Zurians their own natural gas at a nice profit and everybody was happy with the situation except the brothers Masur.
output:  The gas was collected on Zur
options:  The gas was collected on Zur  The gas is from Earth and will not power Zurian machines  The gas will be replaced by a new type of gas that Zurians will need to purchase in the next decade  The Earthmen are not selling gas; rather, a material that causes machines to break