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 .
According to the above context, choose the best option to answer the following question.
Question: why did he come in at a fifth of the national average for his carbon budget ?
Options:
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