Question

Use a singular verb with sums of money or periods of time.

Ex) Ten dollars _____ a high price to pay.

Ten dollar is a sum of money, so you have to use a singular verb. In this case, the subject acts as a unit.

I'll give you another example.

ex) Ten years is a long time.

In this sentence 'ten years' is a period of time. When a subject is a period of time, you have to use a singular verb though the subject has a plural form.

Look at the exception.

ex) Ten years have passed since he died.

In this case, you should use a plural auxiliary verb, 'have' because ten years indicates the process of time.

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Hello. Good to see you again.
Is my explanation of grammatical points correct? If I didn't explain well, would you correct them?

Answer 1

Everything looks good except the end of the last sentence. I'd say, "... because 'ten years' indicates a plural number of years not being used as a unit."

=)