Each termite produces only about half a microgram per day, but there are so many of them in the world that together they produce about 20 million tons per year.

• 每只白蚁每天只能产生大约半微克的沼气,但是世界上白蚁的数量如此巨大,以至于每年它们产生的沼气多达两千万吨。