The problem SACK is meant to address is this "all or nothing" nature of the plain cumulative acknowledgment.

SACK 要解决的问题普通累积式应答的 “全有或全无”性质。

youdao

Note: If you wish to receive an acknowledgment of your application, please write your name and address and affix stamp below.

注：如阁下希望收到通知确实本中心收妥已递交的申请，请写上姓名及地址连同回邮邮票，以便处理。

youdao

Note: If you wish to receive an acknowledgment of your application, please write your name and address and affix stamp below.

注：如阁下希望收到通知确实本中心收妥已递交的申请，请写上姓名及地址连同回邮邮票，以便处理。

youdao