Which of the Following Strengths Would Competitors Least Likely Be

Which of the following strengths would competitors least likely be able to copy?

A) Mountain Home University begins an evening program for adults in which students take one class two nights per week for one month.
B) Measurement Systems comes out with a blood sugar monitoring device that works with an insulin pump that diabetics already use.
C) Kingdom Investments' chief stock analyst has been able to provide investors with a 20% return on investment for the last 10 years.
D) Choice Brands introduces a new cereal with dried fruit.