Answer: D. Informing the student body about the school's new recycling program.
A website would be particularly effective in this case because the audience that needs to be reached is a large one (the whole student body). Moreover, the topic is one which could be significantly complex. Students will probably use it as reference, so they will need to check it several times. A website would make it easily accessible and always available.
Answer: informing the student body about the schools new recycling program
