The fashion of bell-bottomed trousers has become out of date.

The correct answer is C. Obsolescent.

• Preposterous means ridiculous or absurd.
• Debilitating means causing or tending to cause weakness or disability.
• Obstreperous means noisy and difficult to control.

Bell-bottomed trousers are a type of trousers that are wide at the bottom. They were popular in the 1960s and 1970s, but they are no longer in fashion. They are considered to be obsolete, which means that they are no longer used or produced.