 }
 
 //: `GroupAdd` is a vanilla class that manages an operation queue and multiple `SumOperation`s to calculate the sum of all the pairs in the input array.
+//: > __TODO__: There are 3 places in this class that you need to add implementation
 class GroupAdd {
   let queue = NSOperationQueue()
   var outputArray = [(Int, Int, Int)]()

  
  func start() {
    // TODO: implement this
    queue.suspended = false
  }
  
  func cancel() {
    // TODO: implement this
    queue.cancelAllOperations()
  }
  
  func wait() {

    for pair in numberArray {
      let operation = SumOperation(input: pair)
      operation.completionBlock = {
        // TODO: Implement this
      }
      queue.addOperation(operation)
    }
