I don't understand why the answer to question 20 was D, rather than C, is anyone able to explain?

Thank you :)

(20) Consider the following C code: * void function(void) { fork(); fork(); printf("hello world\n"); } * If the above code executes successfully, which of the following statements will always be true? A. The output "hello world" will be printed once. B. The output "hello world" will appear exactly twice, on two separate lines. C. The output "hello world" will appear exactly four times, on four separate lines. D. The form of the output cannot be determined from the above code.