What is dumping in international trade and how is it viewed by the US law?

Dumping is when a company sells its products in a foreign market at a lower price than in its domestic market.
Dumping is considered a competitive and legitimate practice by most economists.
The US law prohibits foreign companies from practicing dumping in its market and imposes automatic tariffs when such dumping is discovered.
a) Only afirmation I is correct.
b) Only afirmation II is correct.
c) Only afirmation III is correct.
d) Afirmations I and III are correct.
e) Afirmations II and III are correct.