Which of the Following Is an Example of Random Assignment

Which of the following is an example of random assignment?

A) assigning all left-handed participants to a particular condition
B) having participants choose which condition they would prefer to be in and then assigning them to a different condition
C) having participants choose which condition they would prefer to be in and then assigning them to that condition
D) using a random number generator to assign participants to conditions (e.g., odds are in one condition and evens in another condition)