题目

函数y=x的最大值为（ ）A.                  B.0                    C.                     D.- 答案：解析：x＞0时,y=x=≤=.选C.答案：CPaper money was in _____ use in China when Marco Polo visited the country in_____thirteenth century.A. the; 不填 B. the; theC. 不填; the D. 不填; 不填;