Which switch series can function as a modular chassis or a fixed-form-factor stackable switch?

A.
A5820 Switch Series

B.
A7500 Switch Series

C.
A9500 Switch Series

D.
A12500 Switch Series

Explanation:

Reference:http://www.costcentral.com/proddetail/HP_A5820_24XG_SFP/JC675A/11274225/(first
paragraph)