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Please see the following question.

"It means to be seen _______ Virtotech's decision to acquire BHI Industries will result in increased profits.
(a) whether (b)in order that(c) whereas(d)that

The correct answer is (a)whether.

What I want to ask you is not it. Please see the following sentences.

[Q1] I don't know whether it is true. ( Is this sentence correct without "or not"? In usual I've used "whether or not")
[Q2] I don't know if it is true.( Normally I never use "or not" with "if". Normally I use the adjective "curious" together with "if". Suddenly I want to know it. In this case can I use "if" instead of "whether or not"?)

Thank you for your answers in advance.
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Son James"It means to be seen _____ Virtotech's decision to acquire BHI Industries will result in increased profits.
That sentence sounds unnatural to be. It should read, 'It remains to be seen ...''

I don't know whether or not it's true.
I don't know whether it's true or not.
I don't know whether it's true.
I don't know if it's true or not.
I don't know if it's true.
I don't know if or not it's true.

The first five are fine.
Comments  
Thank you so much for your answers,FivejedjonEmotion: embarrassed. This answer of yours is very helpful for me.