What is the equivant of Variant data type in C#.NET?

Question

Hi,

I'm using a COM object which has a method with 5 arguments, 3 of them being optional (below).
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COM Object method

objLibrary.CreateObject(ObjType, ClassIdent, [Option], [OptionEx1], [OptionEx2])

Parameters:
ObjType - idmObjectType
ClassIdent - Variant.
Option - Optional. Variant.
OptionEx1 - Optional. Variant. 
OptionEx2 - Optional. Variant. Not implemented.
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My code:

IDMObjects.Document objDoc;

objDoc = (IDMObjects.Document) (objLibrary.CreateObject(IDMObjects.idmObjectType.idmObjTypeDocument, objClsDesc, variant1, variant2, variant3));

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In VB and C++, I can ignore the 3 optional arguments ie. CreateObject( arg1, arg2), but in C#.NET I need to supply 5 arguments. I tried putting null, empty string, zero into the optional arguments (variant1, variant2, variant3) but I keep on getting "Bad Variable" error.

I also tried declaring a variable of type Object:
Object variant1 = new Object()
and feed that into the optional arguments, but didn't work either.

Could anyone please help me?

Thank you so much in advanced.

Regards,
Tina