16. In atom theory, the center of the atom called _____?
a. Nucleus
b. proton
c. electron
d. neutron

17. A kind of source that has two or more cells.
a. Battery
b. DC source
c. AC source
d. transformer

18. A source that allows the current to flow in one direction.
a. AC source
b. DC source
c. Transformer
d. Battery

19. A source that allows the current to flow in different direction with the same time.
a. AC source
b. DC source
c. Transformer
d. Battery

20. In Electric power generator AC means?
a. Access Current
b. Alternative current
c. Anti-current
d. Alternating current​