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Inventories
12 Months Ended
Dec. 31, 2019
Inventories [Abstract]  
Inventories
5. Inventories

 

Inventories as of December 31, 2018 and 2019 consisted of the following:

 

   December 31,   December 31, 
   2018   2019 
Raw materials  $1,675,383   $482,836 
Work in progress   2,737,415    1,254,490 
Finished goods   5,209,563    6,929,388 
   $9,622,361   $8,666,714 

 

During the years ended December 31, 2018 and 2019, write-downs of obsolete inventories to lower of cost or net realizable value of $160,469 and $834,362, respectively, were charged to cost of revenues.