【简答题】Natural rubber is obtained from rubber trees as a white,milky liquid known as latex.This is treated with acid and dried,before dispatched to countries all over the world.
【单选题】根据下列文章,请回答 51~65 题。 The Development of Rubber Here is the story of rubber. From the earliest time it was common knowledge _________ (1) the Peruvians that when a cut was made in the outside skin of a ...