Until the start of the Industrial Revolution, mankind was poor, hungry, and constantly at the _______ of disease and natural disasters.
1. He kept his head _____ water when he began to learn swimming, but he raised his head now and then
100. The visitors _______ the castle are asked not to take photographs.
99. If you study harder, you will catchthe others in the class.
98. We have friends ____ the world.
97. When he was in America, he made a journey of seven hundred miles _____ purpose to get a glimpse of the Niagara Falls.