Choose the correct preposition

1. There's a poster
   [on|in|under] the wall.
2. There's a garden
   [in|behind|under] the house.
3. There are some flowers
   [on|next to|in] the vase.
4. There's a tree
   [under|behind|in front] of the house.
5. The cat is
   [in front|in|next] to the sofa.