Answer:
One who uses his or her voice in favour of something
Explanation:
This sentence refers to the fact that the 'teen hero' is willing to stand up for any wrong doings against nature, he wants to support this cause, and makes this desire his strenght. His determination benefits nature and his 'voice' makes it be heard by people. It is almost as if he speaks on behalf of it.
The word 'advocate' doesn't mean 'one who is empty of passion for the future' but quite the opposite. It can clearly be noticed that the boy is passionate about this cause and is putting in the effort to cease all abuse towards nature.
It doesn't mean 'one who goes toward joining the government'. The question wants you to identify the meaning of 'advocate' from the very first sentence. It doesn't have anything to do with the government since anyone can support a cause without having a high position of power.
Do not be mislead by the other 'advocate' word which is used later on, where the boy sends a letter to his state politicians, asking for their financial aid towards 'the local river cleanup effort' .
'One who puts together efforts to fight progress'. This cannot be the meaning of the word because the boy is a 'hero' who wants progress made towards a good cause. He considers it to be his mission and he won't back away from any challenges he might have to face. He doesn't 'fight' progress, he is not against it - he actually wishes to 'be a benefactor to nature' instead of 'subjecting it to abuse'. He wants people to realise that they have a choice in the matter, and to contribute to keeping nature clean.
