The cattle are grazing in the ground.
in my book the same sentence is given as the cattle were grazing in the field
i think there is no mistake
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we cannot use is
it is always in plural as per my book
first you have written something else
and now you have changed
first you have written is
ThereĀ is no mistake in this sentenceĀ 
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but i posted later
but you didn't knew
you wrote after me
you didn't even knew the answer
then explain