3182
For simplicity , we consider here two basic scenarios : ( 1 ) The motions of the source and / or receiver are exactly along the line connecting them ( longitudinal Doppler effect ) , and ( 2 ) the motions are at right angles to the said line ( transverse Doppler effect ) .
 Doppler, Doppler
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: location, person, organization 
Text: {0} 
Answer:
 Doppler, Doppler