Which thesis statement is the right scope for an expository composition on skyscrapers?

a. skyscraper designs have become more impressive in the last century.
b. skyscrapers create an artistic flair in the cityscape.
c. the empire state building is a 102-story skyscraper in new york city, new york.
d. the empire state building stood as the world's tallest man-made structure for 23 years

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.

this is what i put and it was correct

it's a way for authors to communicate with reader in this time period. books from the past can teach us about life.