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Inventories
12 Months Ended
Dec. 31, 2020
Inventories [Abstract]  
Inventories
5. Inventories

 

Inventories as of December 31, 2019 and 2020 consisted of the following:

 

   December 31,   December 31, 
   2019   2020 
Raw materials  $482,836   $757,857 
Work in progress   1,254,490    2,338,342 
Finished goods   6,929,388    2,156,646 
   $8,666,714   $5,252,845 

 

During the years ended December 31, 2019 and 2020, write-downs of obsolete inventories to lower of cost or net realizable value of $834,362 and $1,450,182, respectively, were charged to cost of revenues.