seinen or seine Schlüssel accusative plural? Module 13.5

The sentence is: 

Thomas hat gestern seinen Schlüssel verloren. 

The translation is: 

Thomas lost his keys yesterday.  

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Shouldn't the translation be? 

Thomas lost his key yesterday.  

Or should the sentence be? 

Thomas hat gestern seine Schlüssel verloren. 

Seinen Schlüssel certainly looks like singular accusative, but I am not certain if it is a mistake or intentional to translate it as plural as it is more usual to say" I have lost my keys" rather than “I have lost my key”. If it is intenional perhaps they should add a literal button to clarify.

That's a plausible and acceptable answer. If that is the intention, then you're right, the "Lit" indicator is definitely called for. 

Hallo gottahaveajava und sfpugh,

thank you very much for letting us know about this! We have changed the sentence to “Thomas lost his key yesterday." Our apologies for any confusion this may have caused.

Grüße,

Julia
 

Wow, Julia, that was quick. Great stuff! 
 

Thanks,

gottahavea