What is SCRUM?

I believe that release planning and iteration planning are both required. You can have a plan in mind and think about every aspect of it then when it is time to be released, will you just release it depending on what you think will be most ideal for you? It does not work that way, unfortunately.

What you need to do is to plan both things which means that D. is the answer to this question. Release planning will hold information about when the features will be implemented well. It is also needed in order to monitor the project well. If this would not be planned, it can be problematic for the whole plan. It is always ideal that both will be planned instead of just doing iteration planning.