79739
Planetary nebulae are classified by different authors into : stellar , disk , ring , irregular , helical , bipolar , quadrupolar , and other types , although the majority of them belong to just three types : spherical , elliptical and bipolar .
 bipolar
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: media, plant, vehicle, astronomical object, time, disease, animal, location, person, organization, mythical figure, food, biology, geographical phenomenon, instrument, event 
Text: {0} 
Answer:
 bipolar