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 .
why did he come in at a fifth of the national average for his carbon budget ?
Pick the best answer from the following options:
- he wants to stop being an environmentalist
 - he believes carbon contains the cure for the environments issues
 - he spends carefully because he knows about carbon 's effects on the environment
 - None of the above choices .


he spends carefully because he knows about carbon 's effects on the environment