Identify the best definition of planning

Explanation :
Planning is defined as setting the objective organization's mission and deciding how to achieve those objectives.
It shows that planning is more than just devising ways to achieve an organization's objectives (B).
It also shows that planning is not limited to just formulating plans, but extends to carrying out and controlling plans as well (A).
Finally, this definition also shows that it is not limited to planners and planning departments (C), but can be carried out by anyone at any level in an organizationally

Final answer
Hence, the correct option is D. Setting an organization's objectives and the means of reaching them.