I don’t know the answer. Pls help. Is it A, B, C, or D. Best for fluent Spanish speakers

Answer: D. Para, por
Para tener un planeta limpio, todos tenemos que preocuparnos por cuidar el medio ambiente.
To have a clean planet, we all have to be interested in taking care of the environment.
[tex]\textit{\textbf{Spymore}}[/tex]