They could not continue their method of producing surpluses. 
ðeɪ kʊd nɑt kʌntɪnju ðɛɹ mɛθʌd ʌv pɹʌdusɪŋ sɜ˞plʌsɪz. 
 Indian's voice is very clear and very monotone in this recording, with a very close-sounding tone. The lack of background noise allows the words to be easily discerned.