Explanation
This book heavier than is that one. یہ کتاب اس سے زیادہ بھاری ہے۔
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according to the above statement" the book is more heavy than the other one",
if we choose the word 'more heavy' it will be inappropriate.
so the correct word to describe the weight of the book is 'heavier than.
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ND4-12-2022