Step 1: Assess option A: for small subgroup sizes, the relative efficiency of the sample range as an estimator of the process standard deviation stays close to that of the sample standard deviation itself, so their control limits and out of control signals track together. This makes option A true.
Step 2: Assess option B: the sample range needs only two order statistics (maximum and minimum) rather than every observation squared and averaged, so it is quicker and simpler to calculate on a production floor, making option B true.
Step 3: Assess option C: because of this computational simplicity, plotting an R-chart repeatedly (say every hour on a factory line) costs less time and manpower than plotting a \(\sigma\)-chart, so option C is also true.
Step 4: Since options A, B and C are all individually correct reasons for preferring the R-chart over the \(\sigma\)-chart for small samples, the combined choice, All of these, must be selected.
\[\boxed{\text{All of these}}\]