Syntax

Thank you, GPY.

I understood now. The problem was/is that the only word was mentioned in the preceding sentences in that text was "flammable". Then, in the following sentence "they" was used. I think it was a mistake, and there, "it" should have been used instead. Many times, I have found mistakes even in textbooks. Textbooks are written by humans and himans make mistakes??.

I troubled you. Thanks for your explanation.

Kind regards,

JA