In Visual Basic if we declare a variable without any data type by . . . . . . . .this the data type is assigned as default..

string
boolean
variant
date

The correct answer is C. Variant.

A variant variable can store any type of data, including numbers, strings, dates, and objects. It is the default data type in Visual Basic.

A string variable can store a sequence of characters.

A boolean variable can store either the value True or False.

A date variable can store a date and time.

A variant variable is more flexible than a variable of a specific data type, but it is also less efficient. This is because the compiler has to check the type of each value that is assigned to a variant variable, and it has to convert the value to the appropriate type if necessary.

For example, if you assign a number to a variant variable, the compiler will convert the number to a string. If you assign a string to a variant variable, the compiler will convert the string to a number.

If you are not sure what type of data you will be storing in a variable, it is best to use a variant variable. However, if you know that you will only be storing a specific type of data, it is more efficient to use a variable of that type.