填空题 Look at the four squares, , , , and , which indicate where the following sentence could be added to the passage. Where would the sentence best fit?
It is the only method available for obtaining a variety of colors in bamboo.
For centuries, bamboo has provided building materials for Eastern cultures. Now it is becoming more popular and available in the West, particularly as a substitute for expensive hardwood flooring. As a flooring material, natural honey-colored bamboo is more stable than carbonized bamboo. Carbonizing is a technique of steaming and pressurizing the bamboo to introduce carbon fibers that darken the original material. However, it lowers the hardness factor, making the darker bamboo more susceptible to damage.