有關Present Perfect Tense 問題想問問

參考資料：
http://blog.xuite.net/zlee814/eng/66787323-%E7%8F%BE%E5%9C%A8%E5%AE%8C%E6%88%90%E5%BC%8F(Present+Perfect+Tense)

2015-07-01 14:02:34 補充：

圖片參考：https://s.yimg.com/lo/api/res/1.2/ZQit8r6YM3UMER1bF6V.OQ--/YXBwaWQ9dHdhbnN3ZXJzO3E9ODU-/http://i.imgur.com/ZH9B85L.gif

你好～

你可以先看看我放在意見欄的參考資料：

現在完成式(Present Perfect Tense)的用法﹕ 描述由過去直至現在的事 例﹕I have learned English for ten years. (我過去十年一直在學英語。)過去發生的事例﹕I have already done my homework. (我已經做完功課。) 重點提示﹕凡表示過去發生的事而沒有明確的過去時間，則用現在完成式。如有明確時間如yesterday, last night 等則需要用過去式。
因此，對於你的句子
"Mum, I have boiled the water to kill germs."，
當中沒有明確地指出時間（雖然你本身知道時間是六時，但句子中沒有指出），所以使用 present perfect tense (現在完成式) 是可以的，在時態上並無不妥。



圖片參考：https://s.yimg.com/rk/HA00430218/o/639306524.jpg

我媽媽叫我係今天下午六點之前煲熱d水殺死水中既菌。咁我剛剛煲完d水，我同媽媽講"Mum, I have boiled the water to kill germs." 有無唔妥。
Addition: " Mum, I have boiled the water to kill off germs"

雖然先後有網民提醒他
遺憾 TOMING88 直到現在對 Present perfect 和 since 一竅不通
一有 time, 他非常混亂

I have boiled the water since 6pm. ~ 錯
I have boiled the water before 6pm. ~ 錯
"咁我剛剛煲完d水"
怎可以說 " I have boiled the water since and before 6pm. "

Too much not essential, not useful things that can't be added to the sentence.
eg:-Mum,I have just boiled the water.
Mum, I have already boiled the water.
Mum, I have boiled the water since and before 6pm.

2015-07-04 08:58:17 補充：
"since" when we refer to a point of time in the past.
"for" when we refer to a period of time.