In this task, you will be shown a passage. You need to write a fill-in-the-gap question based on your understanding of the events that might be inferred from the passage. Your question should be answerable based on the passage and only have one correct answer. Show the gap in your question with a _ .
Q: If you've ever hit send on an email only to realise you've sent it to the wrong person, you'll know the feeling of dread that hits the pit of your stomach. But thankfully, for Gmail users at least, there is now a solution to spare any future blushes. Google has made its 'Undo Send' tool an official and permanent feature nearly six years since it launched as an experiment in Gmail Labs. To enable the feature, Gmail users can click the cog icon from their inbox and choose Settings. From there, under the General tab, they tick the 'Enable Undo Send' box and set the cancellation period.The feature was previously only available in Gmail Labs and the Inbox appGoogle has now added it to Settings menu of the desktop version of GmailOnce enabled, people can add up to a 30-second delay to sent messagesClicking 'Undo' within the set time prevents the message being delivered
A: 
Google added the feature to _ - a scheme the firm describes as 'some crazy experimental stuff' - in March 2009.