In Cities with Rent Controls, the Actual Rents Paid Can

In cities with rent controls, the actual rents paid can be higher than the legal maximum. One explanation for this is

A) landlords are allowed to charge more than the legal maximum on some apartments so long as they charge less on others.
B) because there is a shortage of apartments, tenants often are willing to pay rents higher than the law allows.
C) rent control laws are so complicated that landlords and tenants may not be aware of what the legal price is.
D) the legal penalty landlords face for charging more than the legal maximum rent is less than the revenue earned by charging their tenants more than the maximum rent.