After her son died in a car accident, the old lady would sit at the window, ______ out and _______ in thought.
The United Nations is trying to free the world________the threat of war.
Traffic conditions in Beijing________for decades.At first people only complained about jams during rush hours,but today every hour is rush hour.
It is difficult for children to change their eating habit later in life.________,parents should encourage healthy eating from an early age.
It is well known that knowledge is________treasure house,but practice is________key to it.
The young man was modest and worked hard,and gradually managed to________his status.