有關現在完成式問題詢問

Note that the word "ever" is used at am:-
Have you ever known (our) buying for the cake ?

Note that the word "since" is used at pm:-
I have bought the cake since this morning, Mary.

The experience and time of the cake being bought were known to Mary with thanks ,to show present result of past action.

"思維混亂 It doesn’t make sense"-this comment also applies to TOMING88's writing:
... (our) buying for the cake ?

I have bought the cake since this morning, Mary.

The experience and time of the cake being bought were known to Mary with thanks ,to show present result of past action...

竟然 Mary 知道你幾時買個蛋糕, 為什麼你還對 Mary 說 "I have bought the cake."?
你下午同 Mary 講. 不是講多謝 Mary 早上陪你去買一個蛋糕, 而是只講你買了個蛋糕. 非常怪, 思維混亂 It doesn’t make sense.

2014-12-26 02:27:42 補充：
我亦有同感
他的兩個句子都是錯
我講得太多, 變成我 crucify 他了

2014-12-26 02:45:28 補充：
謝謝回答者: Hiu Tung 的 contribution

對其他人講:
"I bought a/ the cake this morning " ~ 對, 講這句話時已是下午

如果講話時仍然在早上, 可講 "I have bought the cake." ~ 強調已完成該動作

知道發生時間的事件通常都用過去式表達, 即 I bought a/ the cake this morning.

但如果要強調已完成該動作, 用現在完成式也可以, 即 I have bought the cake.
或者 I did buy a/ the cake.