What Does a Managed (Or Dirty)float Mean

What does a managed (or dirty) float mean?

A) That a country's currency is fixed to the price of gold.
B) That a country's currency is fixed to the value of the U.S.dollar.
C) That a country's balance of payments is persistently in deficit.
D) That the country's central bank fixes the value of its currency.
E) That a country's central bank buys and sells currencies in order to smooth out short-run fluctuations in its own currency.