Which of the following reasons may lead to subscriber hook without a dial tone? (Multiple choice)

In UA5000 of PVM as the main control board machine box, which of the following statement about the user board is correct?

VDSL2 on a pair of twisted pair provides vertically symmetrical/asymmetrical transmission rate, transmission distance of about 3km, the maximum descending rate of 52M (symmetric rates), the maximum upstream rate of 12M (asymmetric rate).

(single) Is the following description correct? The MA5600 uses the service-port command to create an xDSL service flow. The service flow is classified into single service and multiple services. If you select single-service or do not enter multi-service, the default is single service.

(multiple) Which of the following reasons may cause a voice user to pick up the phone without a dial tone?