题目

Before 1776, _________ United States was under the rule of _________ Britain. A . the ... the B . the ... / C . a ... / D . / ... the 答案：B13、已知⊙O的半径为5厘米，若⊙O′与⊙O外切时，圆心距为7厘米，则⊙O′与⊙O内切时，圆心距为3厘米．