The field strength of an alternator may be changed by varying the amplitude of the DC power, supplied to the rotating field by:
1. the use of a field rheostat
2. a reducing gear
3. changes of the input frequency
4. electronic control
a) 1, 2, 3
b) 1, 4
c) 1, 3, 4
d) 2, 3, 4
e) 3, 4
Answer: B