原版书上说，similar to immediate fixed annuity, an ALDA involves permanent exchange of a lump sum of for an insurance contract to pay an income. 所以ALDA和 immediate fixed annuity相似之处在？
李老师基础课上说ALDA既包括immediate fixed annuity, 也包括额外的deferred fixed annuity，例如85岁开始的额外支付。但是原版书看不出来，感觉就是年纪很大的时候的额外支付，请老师分解~
