Which of the following statements are true?a. Strain gauges are based on piezo-resistive effect.b. The strain gauges should have high resistance coefficient.c. The gauge factor is defined as the ratio of per unit change in resistance to per unit change in length.d. Strain gauge should have low value of gauge factor to result high sensitivity.

• A. Only b is true
• B. b and c are true
• C. a and c are true
• D. c and d are true