Which of the following statements best describes the rate at which land subsidence is occurring in mexico city? a. the land has subsided about 10 feet in the last 100 years, and the rate is staying the same. b. the land has subsided about 10 feet in the last 100 years, and the rate is increasing. c. the land has subsided about 30 feet in the last 100 years, and the rate is decreasing. d. the land has subsided about 30 feet in the last 100 years, and the rate is increasing.

The correct option is D.
The Mexico city was built on the ruins of an old lake. The lake was drained in order to provide the needed land for the city and water has to be regularly pump out of the underground aquifers in order to prevent flooding and also to provide drinking water for the city. This affected the supporting soil structure and result in the sinking of the city. The city has sunk by about 30 feet in the last 100 years  and this has caused a lot of damages which are quite expensive to repair.

Transition words are words like first, furthermore, besides, for instance, secondly, as a result using words like those should you write paragraphs showing time. you can start with first and then end with lastly or as a result