Which sentence uses a verb that agrees with its subject?
a.
the snails in the garden moves slowly.
b.
authors of books receives royalties for their work.
c.
the stripes on the american flag are white and red.
d.
a bag of groceries were found outside the store.

The snails in the garden move slowly.

Authors of books receive royalties for their work.

A bag of groceries was found outside the store.
That leaves you with the choice C, which is the correct answer.

D might be a little tricky because of the word 'groceries'. But notice that it says 'a bag' of groceries which indicates that it is singular.

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