What is the Gresham's Law?

When two currencies of equal nominal value but different quality circulate in a country, the weaker currency displaces the stronger currency from circulation.
When two currencies of equal nominal value but different quality circulate in a country, the stronger currency displaces the weaker currency from circulation.
When two currencies of different nominal value but equal quality circulate in a country, the weaker currency displaces the stronger currency from circulation.
When two currencies of different nominal value but equal quality circulate in a country, the stronger currency displaces the weaker currency from circulation.
a) I is correct.
b) II is correct.
c) III is correct.
d) IV is correct.