It's not straightforward. You might start by looking for common themes or messages in 'The Lorax' and non-fiction works, and then finding ways to connect those.
One way could be to draw parallels between the environmental themes in 'The Lorax' and real-world environmental issues discussed in non-fiction. For example, you could compare the fictional deforestation in the story to actual deforestation cases.
The specific process of Xu Fengnian's fusion of the three religions was not clearly described. The search results mentioned that Xu Fengnian had received guidance and help from many masters, including Daoist Kylin, Dragon Tree, Wang Chonglou, and others. They had given Xu Fengnian different opportunities to improve his realm. Among them, Wang Chonglou had imparted the Great Yellow Court to Xu Fengnian, the Dragon Tree had given him a drop of blood, and his senior brother had given him luck. The guidance and help of these masters might be part of Xu Fengnian's integration of the three religions, but the specific process and details were not mentioned. Therefore, he couldn't give an accurate answer to Xu Fengnian's question.
To effectively integrate quotes from a novel, make sure they fit smoothly into your sentence. For example, you can use a lead - in phrase like 'As the author states in...'.
Well, first you need to make sure the outside info is relevant and reliable. Then, find a way to smoothly incorporate it without disrupting the flow of the story.
One way to integrate two stories in one book is to have a common setting or time period. Also, interweaving the characters' lives and their arcs can make the integration more natural. Maybe introduce a central conflict that both storylines contribute to solving.