= Solution
A longer hydrophobic tail makes transfer from water into a <micelle> more favorable, lowering the <critical micelle concentration> within this homologous series. Ranking the four quoted concentrations therefore gives
$$
\boxed{B:\mathrm C_4,\qquad D:\mathrm C_8,\qquad A:\mathrm C_{10},\qquad C:\mathrm C_{14}.}
$$
This assignment uses the chain lengths and concentration ranking printed in the question; it does not identify the compounds by substituting an external table of measured concentrations.
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