The underlined word "upbeat" in paragraph 2 probably means ______.

单项选择题The author believes that more houses were bought last year because______.

单项选择题The weekly unemployment data show that ______.

单项选择题The author discusses computing machines in the first paragraph primarily in order to ______.

单项选择题The author suggests that a mathematician asked to solve a problem in an ill-defined situation would first attempt to ______.

单项选择题According to the passage, scientists are skeptical toward their equations because scientists ______.