you are likely to find Roof in/at/on Mouth. you are likely to find Ladder in/at/on Roof. 
Small is related to Car. Car is the opposite of Boat. you are likely to find Food in/at/on Boat. 
Mouth <--AtLocation-- Roof <--AtLocation-- Ladder 
Small <--RelatedTo--> Car <--Antonym--> Boat <--AtLocation-- Food 