Situation 2

Student A uses a pencil when doing his/her assignment, while student B uses a mechanical pencil to save more trees in order to conserve energy.

Answer:

Bryan: Can I borrow your pencil?
Sisca: Sure, here it is.
Bryan: Thanks. It's a mechanical one, right?
Sisca: Yes. I prefer to use a mechanical pencil since it is environmentally friendly.
Bryan: Why?
Sisca: A mechanical pencil isn't made from wood, so it can save more trees.
Bryan: I see. I agree with you.

Situation 3

Student A usually uses his/her motorbike to school. While student B usually uses his/ her bicycle to school to reduce pollution in order to conserve energy. 

Answer:

Keisya: Let's go to school. We don't have much time.
Paul: Wait, my motorbike is running out of gas.
Keisya: Why don't we just use a bicycle?
Paul: Using a motorbike is faster.
Keisya: I know, but using a bicycle makes us healthy. It also can reduce pollution to conserve energy.
Paul: Alright. Let's use our bicycles then.

( Tribunpekanbaru.com )