单项选择题
Scientists generally agree that the Earth's climate will warm up over the next 50 to 100 years ______it has warmed in the 20,000 years since the Ice Age.
单项选择题 Experts say walking is one of the best ways for a person to ______ healthy.
单项选择题 Physics is the present-day equivalent of ______ used to be called natural philosophy, from which most of present-day science arose.
单项选择题 By the time you arrive in London, we ______ in Europe for two weeks.
