This leaves fertile soil unprotected and prone to erosion.这会让肥沃的土壤暴露在外，使其容易受到侵蚀。You are playing Russian roulette every time you have unprotected sex.行房时不采取避孕措施是非常危险的。Machinery was often unprotected and accidents were fre...
Is the most famous astronomer Ptolemy.最为著名的天文学家是托勒密.Ptolemy charted more than 1000 stars in 48 constella-tions.托勒密绘制了48个星座1,000多颗恒星的星位图。Ptolemy's model of the universe with the Earth at the center.托勒枚的以地球为中心的宇宙模型.Pt...