71681
Possible formation scenarios include a merger with a gas-rich satellite galaxy in a retrograde orbit , or the continued accretion of gas clouds from the intergalactic medium .
 astronomical object: gas clouds
Given options, please tell me the categories of all the listed entity words.Output format is "type1: word1; type2: word2". 
Option: media, plant, vehicle, astronomical object, time, disease, animal, location, person, organization, mythical figure, food, biology, geographical phenomenon, instrument, event 
Text: {0} 
 Entities: gas clouds 
Answer:
 astronomical object: gas clouds