Answer:
d. preserve
Step-by-step explanation:
Option D is the correct answer. "Preserve" is the word that is synonymous to “sustain” as it is used in paragraph 11.
As used in Paragraph 11, sustain refers to keeping the planet fresh in order for it to be beneficial to man. So, "preserve" is the synonym that fits into the paragraph which stills upholds the message that "sustain" is passing across in the paragraph.
Therefore, Option D is the correct answer.