单项选择题 By 1929, two years after the start of the "talkies", motion picture theaters in the United States were attracting 100 million patrons every week.()

单项选择题 According to some biologists, the instinct to care for the young is perhaps the most interesting characteristic of animals.()

单项选择题 California, the first city on the American continent, reached its peak of development and power about AD 1100.()