Question

I am not sure that it is gold change into affirmative sentence

Answer 1

Pikachu! Your answer ^^
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An affirmative sentence is generally positive and simple in the form of:

Subject + Helping Verb + Verb + Obj 

so your answer may go like this:

I am sure that it is gold
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Pikachu! ^^

Answer 2

Hey there!

> What are Affirmative Sentences?

Simply, the just opposite to negative sentences.

=> Sentence given : I am not sure that it is gold

This sentence is in negative sentence

=> Affirmative Sentence : I am sure that it is gold

Hope helped.