To output the value of a multidimensional array, you need to provide the indices for each dimension of the array. Let's go through each option and determine if it correctly outputs the value of a multidimensional array:

A. myArray[1][3]; This option is incorrect because it uses the wrong syntax to access the value of a multidimensional array. In C#, the correct syntax to access a value in a multidimensional array is myArray[1,3], not myArray[1][3]. The correct syntax uses commas to separate the indices for each dimension.

B. myArray[1,3]; This option is correct. It uses the correct syntax to access the value of a multidimensional array. The comma is used to separate the indices for each dimension, and this syntax correctly outputs the value at index 1 in the first dimension and index 3 in the second dimension of the array.

C. myArray{1}{3}; This option is incorrect because it uses curly braces instead of square brackets to access the value of the multidimensional array. In C#, square brackets [] are used to access array elements, not curly braces {}.

D. myArray(1),(3); This option is incorrect because it uses parentheses instead of square brackets to access the value of the multidimensional array. In C#, square brackets [] are used to access array elements, not parentheses ().

Therefore, the correct option is B. myArray[1,3].