Question

How we find error? In grammar in 2 minutes

Answer 1

for this you have to strengthen your grammar by school teachers or if you want shortcut then
there is a site name grammarly where you can correct your grammar mistakes :)

Answer 2

Here's the required answer
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You can only find errors when ur good at English. Try reading passages every day and do some exercises.
This will make u ready to identify the errors. And pay attention to teacher's advise as she would be knowing it the best.
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hope this helps