由1－9组成一个3位数，3位数肯定有数字重复的组合有多少种？（ ）

(单选题)2017年，朝阳区和海淀区的外来人口占两个区的常住人口的比例为（ ）。 (单选题)2016年，北京市常住人口中非外来人口为多少万人？（ ） (单选题)( ) if I had arrived yesterday without letting you know b (单选题)The opening ceremony is a great occasion. It is essential ( (单选题)Quality is ( ) counts most. (单选题)The government has promised to do ( ) lies in its power t (单选题)If not ( ) with the respect he feels due to him, Jack get (单选题)Time ( ), the celebration will be held as scheduled. (单选题)Miss Smith and I keep in touch ( ) writing often. (单选题)During the summer vacation, kids are often seen hanging (