Picket
Monopoly and Oligopoly are two barriers that prevent firms from entering the marketplace.
Shutting it.
Epiglottis
no
Phospholipids in the cell membrane prevent water from entering a cell.
Phospholipids in the cell membrane prevent water from entering a cell.
to close windows and doors
It is to prevent dust from wood from entering your eye.
Phospholipids
To prevent food entering the trachea
To prevent food entering the trachea
The Goalie