Which of the following statements regarding efficiency of electrical machines are true?

[answerhappygod]

(i) efficiency should be calculated by measuring output and input
(ii) efficiency is maximum when constant losses = variable losses
(iii) electrical machines are designed to have maximum efficiency at full load
(iv) electrical machines are designed to have maximum efficiency at near about full load
(v) efficiency should be calculated by measuring their losses
(vi) efficiency is maximum when constant losses = x times of (variable losses)
a) (i), (iii), (vi)
b) (ii), (iv), (v)
c) (i), (ii), (iii)
d) (iv), (v), (vi)