Summarization
Directions: The paragraph is followed by an incomplete phrase or sentence which summarizes the main idea of the paragraph. Spell out the missing letters of the word. 

     Children who are older by a wider gap tend to teach their younger siblings social and manual skills, almost like a third parent, while rivalry is usually greatest when the age difference is small. It is especially so when siblings are under four — they are easily displeased when gratification of their needs is postponed.

The role that age difference p in sibling rivalry.