Чтобы сделать предложение отрицательным,
прибавляем к глаголу NOT ("не")I am=I'm - I am not=I'm not
He/She/It is = He's/She's/It's - is not=isn't
We/You/They are=We're/You're/They're - ... are not=aren't
I am a girl - I'm not a boy She is my friend - She isn't my sister