What will significantly degrade DSL performance, regardless of DSL rate or line length?

What will significantly degrade DSL performance, regardless of DSL rate or line length? Select all
that apply

A.
Microliters installed between a telephone and shared line.

B.
POTS splitters at the subscriber’s end of the DSL line

C.
POTS splitters at the telco CO.

D.
None of the other alternatives apply.