Which of the following statements are TRUE of the $\Delta$ 32 allele in the CCR5 gene?

A)It codes for a mutant protein that is completely inactive.
B)It is a deletion that maintains the reading frame.
C)It provides some protection against HIV progression to AIDS in both its heterozygous and homozygous forms.
D)It is an example of a beneficial mutation.
E)It affects the attachment of HIV to an animal cell by altering one of the viral proteins.