Regarding measurement error, which of the following statements is not correct? Select one: O a. Absolute error is the difference between the measured result and the measured truth value. It has magnitude, plus or minus. O b. Since the true value of a measured value cannot be obtained, the measurement error cannot be obtained in theoretically O c. Measurement errors caused by some special performance habits of experimentalist should be regarded as systematic errors. O d. The use of two instruments with the same model in the measurement should have the equal measurement precision