Which of the following water turbines maintain a high efficiency over a long range of the part load?
1. Francis turbine
2. Kaplan turbine
3. Pelton turbine
4. Propeller turbine
Select the correct answer using the codes given below
a. 1 and 4 b. Only 2 and 3
c. 1, 2 and 3 d. 2, 3 and 4