Summarization：the paragraph is followed by an incomplete phrase or sentence which summarizes the main idea of the paragraph. Spell out the missing letter of the word on your answer sheet.

When infants 18 months old see an unrelated adult whose hands are full and who needs assistance opening a door or picking up a dropped clothespin, they will immediately help. The helping behavior seems to be innate because it appears so early and before many parents start teaching children the rules of polite behavior.
Human beings may be b with the urge to help.