单项选择题
A．represented a great improvement over barter B．permitted easy transportation of wealth C．were made of precious metals D．could become collector’s items
A．how to teach the students in the science class B．whether poetry is difficult for science students C．what to be taught in the humanities class D．why many humanities students find science hard
A．Copernicus did not tell about his discovery until the day of his death B．for many years Copernicus dared to do nothing openly against the Church C．pushed by his friends Copernicus decided to write a book in May 1543 D．shortly before he got back to Poland Copernicus started to work for the Church