单项选择题 Refer to Topic TestKing.com in iPAD document.What happens to the network when TestKingX is reconnected and a trunk exists between the two switches?（）

多项选择题 Which statements are true regarding ISDN channels?（）

单项选择题 Which ISDN device converts the four-wire BRI signals from an S/T interface into two-wire signals of a U interface?（）