Potter, Charles Francis.. <br/><br/>
Can you Say These tongue Twisters?. 

 - Nueva York-US  :   The Reader's Digest Association,   1944. 
 - páginas 30-31 :   ilustraciones full color 
 - Mensual 
 - Vol. 45, no. 271(Nom. 1944) 
 - The Reader's Digest  ;   no.271 .
 - The Reader's Digest Association. .