Which xDSL flavour delivers both downstream and upstream speeds of 1.544 Mbps over two copper twisted pairs?

Which xDSL flavour delivers both downstream and upstream speeds of 1.544 Mbps over two
copper twisted pairs?

A.
HDSL

B.
SDSL

C.
ADSL

D.
VDSL

Explanation:
HDSL – High-Data-Rate Digital Subscriber Line – 1.544 Mbps each way over 2 copper twisted pair
(http://www.cisco.com/en/US/tech/tk175/tk318/tsd_technology_support_protocol_home.html)