today rose is twice as old as Sam and Sam is 3 years younger than Tina. If Rose, Sam, and Tina are all alive 4 years from today, which of the following must be true on that day?
I. rose is twice as old as Sam
II. Sam is 3 years younger than Tina
III. rose is older than tina
B) II only
答案B
没有弄明白，得到的式子是：r=2s s=t-3 所有r=2(t-3)
如果III成立应该有：r>t 即 2(t-3)>t 所以t>6是其成立的充要条件
但是题目中说了4年前三人都活着，也就是说r,s,t 都大于4 那么s=t-3>4 得出t>7显然t>6满足，那么为什么III不对呢？？ | 
