Yes, parts of every underground line on the tube network use stations that are also used by the circular line, and are therefore connected.
Presumably you mean the London Tube? If so, it is the Jubilee Line (silver).
Yes, that is correct. You have answered your own question.
The Circle Line Unfortunately this answer is wrong! According to Transport for London the only tube line to connect all London Underground lines is the Jubilee Line.
District Line
interconnect the different calls through single line
There are 15 Underground station at the Bakerloo line.
On the London Underground map, the Circle Line is coloured yellow.
The Victoria Line.
Green is the District Line
Optical fiber
Hammersmith & City line