In 2007, computer scientist Luis von Ahn was working on converting printed books into a digital format. He found that some
words were distorted enough that digital scanners couldn’t recognize them, but most humans could easily read them. Based
on that ﬁnding, von Ahn invented a simple security test to keep automated “bots” out of websites. The ﬁrst version of the
reCAPTCHA test asked users to type one known word and one of the many words scanners couldn’t recognize. Correct
answers proved the users were humans and added data to the book-digitizing project.
To discuss von Ahn’s invention of reCAPTCHA
To explain how digital scanners work
To call attention to von Ahn’s book-digitizing project
To indicate how popular reCAPTCHA is
Choice A is the best answer because it most accurately states the main purpose of the text. After providing a brief
introduction to computer scientist Luis von Ahn, the text focuses on discussing how von Ahn’s digitization work led to the
invention of a digital security test known as reCAPTCHA.
Choice B is incorrect because the text doesn’t address how digital scanners work. Choice C is incorrect. Although the text
mentions von Ahn’s book-digitizing project, that information is provided as a detail, not as the main purpose of the text.
Choice D is incorrect because the text doesn’t provide any indication of reCAPTCHA’s popularity; instead, it describes
reCAPTCHA’s origin.