问题：

[单选]

The ONS 15216 is a 32-channel system. The ONS 15216 OADMs are capable of adding and dropping one， two， or four channels.
 How are the OADMs provisioned to add and drop specific channels？（）

A .  The ONS 15216 OADM can be provisioned to add/drop one， two， or four channels via Cisco Transport Manager （CTM）.
B .  The ONS 15216 OADM consists only of a four-channel module， and the number of ports utilized determines whether it is a one， two， or four channel OADM.
C .  Three separate OADM modules are available for one， two， and four channels. The wavelengths to be dropped and added are programmable via Cisco Transport Manager （CTM）.
D .  The ONS 15216 OADM consists only of a single-channel module. Two-channel and four-channel support is available by stacking the single-channel module.
E .  The ONS 15216 OADM is available in one， two， four channels.  There are 32 single-channel OADM modules， 16 two-channel OADM modules， and 8 four-channel OADM modules.