Step 1: Understanding control activity. 
  
Control activity refers to the actions taken by management to ensure that plans are implemented correctly and objectives are achieved. These activities often require resources, time, and effort, which makes them costly. Control activities are essential to the functioning of an organization, but they come at a financial cost due to the resources and systems that need to be in place. 
Step 2: Analyzing the options. 
  
(A) Costly: Correct. Control activities require the use of resources, which makes them an expensive aspect of management. 
  
(B) Cheap: Incorrect. While control activities are necessary, they are generally not cheap due to the resources and systems involved. 
  
(C) Uneconomic: Incorrect. Control activities are essential to the proper functioning of an organization and are considered an economic investment, even though they may be costly. 
  
(D) None of these: Incorrect. The correct answer is (A). 
Step 3: Conclusion. 
  
Control activity is generally considered to be costly due to the resources and systems needed. Thus, the correct answer is (A).