Editing: The use of "there is" and "there are"

I see this problem show up so often in my editing.

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There is vs. there are

I understand there's a rule around expletive constructions like there is/there are, etc., that states the subject, which determines the number of the verb, comes after the verb. In that case, shouldn't these following examples all be plural? Can you please explain?

There are a mix of cars in the lot. Here are a range of choices. There are a myriad of options available. Thanks! Robyn Swanson Hansard Services British Columbia Read more at www.copyediting.com

 

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