What is the output of the following code snippet: System.out.printf("%5.3f", 20.0);?

The output of the code snippet System.out.printf("%5.3f", 20.0); is indeed 20.000.

In this format string, %5.3f specifies that the number should be formatted as a floating-point number. The 5 before the decimal point indicates the minimum width for the output, while the .3 indicates that three digits should be displayed after the decimal point.

Since the number 20.0 has only two digits after the decimal place, the format specification requires it to be displayed with three decimal places, resulting in 20.000. The output width is adequately met because the formatted number, including the decimal point and following digits, fits into the specified minimum width, so there will be no additional spaces added.

This makes option D the correct one, as it adheres to the formatting rules specified by the printf function.