Variable is a synonym of Flexible. Flexible is related to Neck. Neck is related to Voice. Voice is a synonym of Gender. 
you are likely to find Poem in/at/on Book. you are likely to find Cow in/at/on Book. Cow is related to Black. 
Variable <--Synonym--> Flexible <--RelatedTo--> Neck <--RelatedTo--> Voice <--Synonym--> Gender 
Poem --AtLocation--> Book <--AtLocation-- Cow <--RelatedTo--> Black 