题目

The invention of barcodes（条形码） is based on a very simple idea. We only need to give each product a specific number and print it. 1 ． It can simply print the number itself. But this can cause problems. For example, an unclearly printed “seven” could look like a “one” to a computer. It’s also true for “three” and “eight”.2 ． We need a better way of printing numbers so that they can be read correctly at high speeds. That’s the problem barcodes solve. Each number in a barcode is shown by seven blocks of the same size.3 ． For example, the number “one” is s方程3x+y=10的正整数解有几组？（　　）A．1组B．3组C．4组D．无数组