He was not as young as Raihan. (Affirmative)

We need to use more renewable energy so that we can reduce carbon emission. (Simple) = We need to use more renewable energy to reduce carbon emission.

He speaks as he thinks. (Simple)  = He speaks his thoughts.

We should develop the habit of buying books. (Interrogative) = Shouldn't we develop the habit of buying books?

He tried very hard but he could not save the boy. (Simple) = In spite of trying very hard, he could not save the boy.

Earthquake is a natural disaster. (Interrogative) = Isn't earthquake a natural disaster?

Earthquake is a destructive natural phenomenon. (Compound) = Earthquake is a natural phenomenon and it is destructive.