In telephony, what do the initials ISDN stand for?

More Questions:

What company helped the US Army Corps of Engineers develop the "walkie-talkie" in the early 1930’s?

Rennet, an enzyme-filled juice from animal stomachs, is used in the making of what?

What letter is displayed on a typical hot-water tap in France?

What physical fitness practice is named for the Sanskrit word for "union"?

A flag flown upside-down is a signal of what?

What gives beer its distinctive bitter flavour?

What book introduced readers to 11-year-old Anne Shirley?

Who wrote the novel "Of Mice and Men"?

What city's opera house does "The Phantom of the Opera" prowl?

Franglais is a blend of French and what other language?

The financial district of Wall Street is located in what city?

Which band's songs include "Forgiven Not Forgotten" and "Runaway"?

Which US President served the shortest term in office?

What cartoon character did artist Matt Furie decide to kill in 2017, after it became associated with white nationalism against his will?

Candy canes are said to have originated from which European country?