Which Best Defines Negative Cooperativity of Rep Helicase from E

Which best defines negative cooperativity of Rep helicase from E.coli?

A) When 1 subunit binds DNA,the other releases from the DNA.
B) When both subunits are bound to DNA,ATP hydrolysis promotes release of both subunits.
C) ATP hydrolysis promotes DNA binding of both subunits simultaneously.
D) Once it binds ssDNA,binding dsDNA is prohibited.