According to janet lever's observations of children at play, gender has little effect on young children. girls spend much more time at play than boys do. boys favor games with clear winners and losers. boys favor games that encourage communication and cooperation.

The answer is:  boys favor games with clear winners and losers
The dominant hormones that resided within the boys influence their tendency to shows aggressive behaviors.
This tendencies could be reflected on their effort to show 'dominance' with one another and games with clear way of determining winners and losers are seen as a medium to achieve it.

Sector is best defined as (part).