The last show of the concert at the Ritz theatre was a fiasco.

The correct answer is A. triumph.

A triumph is a great victory or success. A victory is a success in a battle or other contest. Fruitful is producing or yielding much fruit or other good results. Success is the accomplishment of an aim or purpose.

In the context of the question, the last show of the concert at the Ritz theatre was a fiasco, which means that it was a complete failure. This is not a triumph, victory, fruitful event, or success.