The second option because solar energy is a renewable source which can be used again.
The third option because walking to work or school would mean that you aren’t using Carbon Dioxide (which is harmful to the environment)
And the 4th option because even though using trains and buses uses Carbon Dioxide, more people can go into one transportation (and it’s public) and they don’t need to use vehicles which is mostly for individuals (mostly only one person driving a car. No passengers)
