The last time I checked my carbon budget , I came in at a fifth of the national average . I rarely fly , even when booked to address faraway audiences about my personal obsession , climate change - a subject I ' ve covered in three books . Whenever the word " nuclear " comes up at my talks , a shudder runs through the room . Because everyone knows that real environmentalists loathe nuclear power .

Question with options to choose from: why did he come in at a fifth of the national average for his carbon budget ?
Options are:
[A]. he wants to stop being an environmentalist;
[B]. he believes carbon contains the cure for the environments issues;
[C]. he spends carefully because he knows about carbon 's effects on the environment;
[D]. None of the above choices .;
[C].