38994
Carbon monoxide / oxygen engines have been suggested for early surface transportation use as both carbon monoxide and oxygen can be straightforwardly produced from the atmosphere of Mars by zirconia electrolysis , without using any Martian water resources to obtain hydrogen , which would be needed to make methane or any hydrogen-based fuel .
 Mars
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: location, person, organization 
Text: {0} 
Answer:
 Mars