Question

1. Lyft began a partnership with rental car company Sixt to let users access rental cars.
2. Lyft began a partnership with a rental car company Sixt to let users access rental cars.
3. Lyft began a partnership with the rental car company Sixt to let users access rental cars.
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Which one do we have to use in the sentences?
1. rental car company
2. a rental car company
3. the rental car company

Answer 1

Since you are naming the company, use #3.
Also, there should be commas before and after "Sixt" since it's an appositive.

Answer 2

#1 is also often used
#2 would definitely require commas.