Read the following passage and mark the letter A, B, Cor D to indicate the correct answer to each of the questions from 21 to 25.

The Twin Towers

The side-by-side towers in New York City, which were home to Manhattan’s World Trade Center, were more commonly known as the Twin Towers. Each skyscraper was an incredible one hundred and ten stories high. Then, on September 11,2001, the World Trade Center was attacked by terrorists. What happened on that date in history should never be forgotten.

The attack on September 11th was not the first time the area had been targeted. In 1993, a bomb had been detonated in the North Tower. This explosion killed six people and injured thousands of others. The tower, however, was able to withstand the explosive power of the blast.

In 2001, both towers were attacked. Two planes were flown directly into the buildings. The effect of these attacks was immediately catastrophic. Neither building was built to withstand such structural damage, and the collapse of each building was imminent. The South tower fell in less than one hour after being attacked, and the North tower collapsed soon afterwards. Both towers were completely gone. The land where the World Trade Center once stood is now known as Ground Zero. The day when the towers were attacked is remembered as one of the most infamous days in America’s history.

What is most likely the reason the World Trade Center buildings were called the Twin Towers?

The underlined word "detonated" most probably means ________.