Reading Comprehension

Read the text and answer the question.

When a large company sends an email to millions of customers, it cannot simply press send and hope for the best. Instead, marketers often run what is called an A/B test. They write two versions of the same message, perhaps with different subject lines, and send each version to a small group first. Software then tracks which version more people open and read. The winning version is sent to the remaining, much larger audience. This careful approach reduces guesswork and helps companies learn what wording appeals to their readers. The drawback is that testing takes time, so it suits planned campaigns rather than urgent announcements.