Read this line from "Empire State Building." It's lonely up here without my big twin brothers,

the World Trade Center Towers.

Which fact is most important for readers to know in order to understand the significance of this line?

The World Trade Center Towers were important office buildings.
The World Trade Center Towers were extremely tall.
The World Trade Center Towers fell on September 11, 2001.
The World Trade Center Towers were built in the early 1970s.

the answer is b just took the tested

the present continuous is a verb tense which is mainly used to indicates that an action is in progress at the moment of speaking.  

it is formed using: person + verb to be (am/is/are) +verb + - ing form  

example: i am studying at this moment .

in addition, the present continuous is also used in order to express things that will or will not happen in the near future.

example: i am having dinner with some friends tonight.

the speaker sometimes   uses it   to express that an action is repeated and it causes irritation on the part of the speaker

example: my sister is constantly complaining about everything.