`1.` S + tobe + the + (short adj) + est + in/on...

`-` She is the shortest in the group.

`-` The building is the tallest on the block.

`-` He was the fastest in the race.

`-` My cat is the fattest in the litter.

`-` This is the cleanest room in the house.

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`2.` S + tobe + the most + (long adj) + in/on...

`-` She is the most beautiful girl in town.

`-` That movie is the most boring I've ever seen.

`-` This is the most delicious cake I've ever tasted.

`-` He is the most intelligent student in the class.

`-` This book is the most interesting one on the shelf.