Answer:
Both screen time is harmful to the brain and Smoking is terrible to you health
Step-by-step explanation:
An argument offers both sides to an topic. For example: should healthcare be free to everyone. Here you can argue for it ( it is not affordable for everyone who needs it) or against it (taxpayers should not have to pay for someones medical that they don't know).
Writing about your dog, bike rides and living in Boston don't offer two sides to an argument. These would more than likely be narrative essays(storytelling).
However, if you must pick one I would suggest screen time because there is more information on it and you can write a solid argument.