Choose the correct form

1. She is [the most|the least] hardworking girl in the class. She never does her homework.
2. This is [the most|the least] expensive dish I have ever eaten. It costs three full meals.
3. This was [the most|the least] productive workshop. I got a lot of useful information.
4. Who is your [most|least] favourite singer? The one you really don't like.
5. Look at the menu! This is [the most|the least] mouthwatering picture. Let's order this dish!
6. This is [the most|the least] expensive thing I have ever seen. Don't buy it. It must be of poor quality.