The Indexof method returns . . . . . . . . value.

The correct answer is: A. Integer

The IndexOf method returns the index of the first occurrence of a specified value in a string. If the value is not found, the method returns -1.

The Boolean option is incorrect because the IndexOf method does not return a Boolean value. The Void option is incorrect because the IndexOf method does not return a void value. The String option is incorrect because the IndexOf method does not return a string value.

Here is an example of how to use the IndexOf method:

string str = "Hello, world!";
int index = str.IndexOf("o");
Console.WriteLine(index); // Output: 3

In this example, the IndexOf method returns the index of the first occurrence of the letter “o” in the string “Hello, world!”. The index is 3, which is the position of the letter “o” in the string.