Select the correct statement$($s$)$ regarding DCE and DTE interfaces.

a$.$ DCE and DTE interfaces can never exist on a single device. The device must either be a DTE or DCE device

b$.$ In order to establish the correct flow of data, DTE interfaces must be connected to other DTE interfaces. Similarly, DCE interfaces must be connected to other DCE interfaces

c$.$ DCE and DTE describes the device type and not the interface nor direction of data flow

d$.$ A DTE interface must be connected to a DCE interface unless a cross$-$over cable is used