If you have this option, you may want to activate the Word Suggestion option under Settings for your keyboard. As long as you correctly start with the word you want, it shows options for words correctly spelt esp. those you tend to use a lot. Just be careful not to get too dependent on it. Hope that helps. If English is not your primary language, try to add English as a keyboard language. Hope this helps.
Yet again Duolingo shows their lack of idiomatic usage, and understanding of common phrases. In conjunction with others who have commented I am annoyed that the commonly used phrase "take lunch" as opposed to "have lunch" or "lunch" has been rejected as wrong by the robot in charge of assesment and marking. To take lunch, dinner or any other meal or form of repast is COMMON USAGE in english language. One does not merely have a meal, one takes a meal, otherwise how can a person actually consume something, in this case a meal. To have something is to possess it, hold it, use it; one does not consume when one has something. To have implys ownership, not consumption. The Oxford English Dictionary define have (1st definition) as "possess, own, or hold"; whereas they define take (1st definition) as "reach for and hold with one's hands".
That is an English way of wording things which is not necessarily easier. In other languages, they don't "have" lunch". They "eat" lunch. They take lunch. or They lunch.
No, simply because i don't think many people would climb up a building to sit on the restaurant roof to eat their lunch, whereas "at the" is at the actual restaurant, therefore either inside it or out the front where sometimes places put tables. To put it simply, "on the" would be on top of the building, and "at the" would be directly in/out the front of the building, in this case restaurant. Sorry for giving a long explanation but i hope it helped :)
I put 'they are lunching at the restaurant' Collins dictionary definition of the verb 'to lunch' = When you lunch, you have lunch, especially at a restaurant. So Duolingo needs to realise that 'to lunch' is as acceptable for 'to have lunch' as 'to dine', which they regularly accept from me for 'to have dinner'. Do Duolingo ever correct their mistakes?