那句嘅if 咩意思？

Both works.

"Let me know" is the key of the sentence. "If" simply sets the condition, which it can mean both a hypothetical and whether.

a is collect .

"Both works."

How "reckless" to make such a careless mistake !!!

2015-05-08 01:10:09 補充：
If you want to know the answer of a question "Are you interested?", you should use "whether ... or not" instead of "if" that would only give a conditional meaning when using verbs other than questioning verbs.

Let me know whether you're interested or not.

Let me know if you're interested in joining the club.

Only "b." (if 解作是否，所以可以用whether 代替) is correct.


When "if " and "whether" are used in reporting questions (which expecting Yes or No answer), they must be used after verbs like "ask," "know", "find out", "wonder", etc. to introduce one of two or more possibilities.

"let me know" = "tell me" in meaning, and it is used rather in imperative mood than in interrogative mood. That said, "let me know" cannot be used to ask for a choiceor to cast a doubt. This convention comes very naturally especially for the native speakers and they will not wrongly interpret the meaning of the sentence.

They would rather say in two ways (indirect and direct):
1. I don't know if you're interested in joining the club. (doubt - interrogative)
Please tell me if you are interested. (imperative - conditional)

2. Are you interested in joining the club? (direct question)
Let me know! (imperative)

2015-05-03 01:49:00 補充：
知足常樂 is also correct to use "whether" (more formal) instead of "if" to get rid of confusion 歧義. However, I suggest it'd better add the conjunction "as" in front.

~ Let me know as to whether you're interested in joining the club. (as to = concerning)

2015-05-03 02:46:10 補充：
Sorry, my answer was meant to be "a." (if 解作如果).

I have explained why "b." cannot be the answer.

2015-05-03 02:48:38 補充：
The answer is : "a." (conditional sentence)

Let me know if you're interested in joining the club.

2015-05-03 03:04:35 補充：
You can ask someone to give you the answer of a question, by saying:

~ Let me know what time you'll come.
~ Let me know how you've done it.
~ Tell me which one you prefer.
~ Tell me why you're not coming.

兩者皆可～

所以如果你希望寫出來沒有歧義（即一句多義）的話，你可以寫：

a.
If you are interested in joining the club, let me know.

b.
Let me know whether you're interested in joining the club.

2015-05-03 02:43:59 補充：
Thanks Julie!

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