单项选择题In 1845 Sarah Mather invented a submarine telescope that could be used to locate and study underwater objects.
单项选择题Frostbitten fingers and toes should be treated with lukewarm water.
单项选择题Youth hostels provide inexpensive lodging for young people throughout the United States and in other countries.
单项选择题National forests make money for the government through the sale of trees for lumber.