问题如下：
Followings are several observations about annuities, how many of them are correct?
I. With immediate fixed annuities, an individual trades a sum of money today for a promised income benefit for as long as he or she is alive.
II. The income yield for a life-only immediate annuity is lower for an older people than for a younger people.
III. Both deferred and immediate annuities provide the same flexibility concerning access to income benefit.
选项：
A.I only
B.I&II
C.All of them are correct
解释：
A is correct.
考点：Annuities
解析：I. 第一个observation的说法是正确的。
II. 对于life-only immediate annuity来说，预期寿命越短，年金income yield越高。因此，相比年轻人，老年人的收益会更高。
III. 延期年金是指保险合同成立生效后且被保险人到达一定年龄或经过一定时期后，保险人在被保险人仍然生存的条件下开始给付年金的年金保险, 而即期年金是指在投保人缴纳所有保费且保险合同成立生效后，保险人立即按期给付保险年金的年金保险。
老师你好，请问第三个表述中灵活性是指什么？是可撤销？收益会随着市场改变而改变还是什么？如果都是fixed的话，那在灵活性上应该没差别吧
