you are likely to find Illness in/at/on Brain. Illness is a synonym of Disease. you are likely to find Disease in/at/on Lab. Lab is related to Doctor. 
Rank is related to Soldier. Soldier is related to Shoulder. 
Brain <--AtLocation-- Illness <--Synonym--> Disease --AtLocation--> Lab <--RelatedTo--> Doctor 
Rank <--RelatedTo--> Soldier <--RelatedTo--> Shoulder 