是否 whether,whether or not
保存 keep,save
贺卡 greeting card(s)
完全是 is entirely,is totally
个人的事情 up to you,your business,your decision,a personal decision,personal business
放在一起：
是否保存贺卡完全是个人的事情
Whether or not you save the greeting card is entirely your business
Whether to save the greeting card or not is entirely a personal decision
我比较喜欢第二句
如果贺卡是复数,用 greeting cards
希望帮到了你,
我是加拿大人,前英语老师.