Read the following passage and choose the best answer (A, B, C, D):
The ubiquitous bar code, developed more than twenty years ago, is not a stagnant product. On the contrary, the technology has been improved so that it can be used more efficiently. Much less expensive than a computer chip, the bar code can hold more information than it had in the past by adding a second dimension to the structure. The bar code consists of a series of parallel vertical bars or lines of two different widths, although sometimes four widths are used, printed in black on a white background. Barcodes are used for entering data into a computer system. The bars represent the binary digits 0 and 1, just like basic computer language, and sequences of these digits can indicate the numbers from 0 to 9, which can then be read by an optical laser scanner and processed by a digital computer. Arabic numbers appear below the code. The traditional bar code has been used to monitor skiers at ski lifts and to determine price and perform inventory control on groceries, drugs, medical supplies, manufactured parts, and library books to name a few. The bar code used on grocery products, introduced in the 1970s, is called a universal product code (or UPC) and assigns each type of food or grocery product a unique code. The five digits on the left are assigned to a particular manufacturer or maker and the five digits on the right are used by that manufacturer to identify a specific type or mark of product. Traditional single dimension bar codes are not readily customizable because there is little extra space. The two-dimensional bar code, with an information density of 1,100 bytes, allows a considerably greater amount of information to be coded than does the traditional bar code, including customized information. [A] It also has built-in redundancy, meaning that the identical information is duplicated on the same code. [B] Therefore, if the code is damaged, it can still be read. [C] The technology even allows pictures or texts to be contained within the code, as well as bar code encryption. [D] The new technology dramatically reduces the errors of the single dimensional bar code and reduces the enormous costs that some companies have reported in the past.
4. The author's main purpose is to describe:
