Misc: what is the last name of singer Madonna?

Questions

Richard Nixon was the 1st U S president to visit China in february of what year?

River in the central U S, the largest & most important river in North America?

Roads on which trains of freight & passenger cars, drawn by locomotives, travel on tracks formed by pairs of parallel metal rails (locomotive)?

Robert Baden-Powell founded this group in 1907?

Rock, the original composition & texture of which has been altered by heat & pressure deep within the earths crust?