Mark the letter A, B, C, or D to indicate the sentence that best combines each pair of sentences in the following questions.

Question. Wastewater is treated and turned into drinking water. This is done to ensure there is no shortage of fresh water.

A. If you don't use your mobile phone a lot, you don't have large phone bills.

B. If you didn't use your mobile phone a lot, you wouldn't have large phone bills.

C. If you don't use your mobile phone a lot, you won't have large phone bills.

D. If you won't use your mobile phone a lot, you won't have large phone bills.

A. If I insert a CD, my computer will crash.

B. If I insert a CD, my computer crashes.

C. If you want my computer to crash, insert a CD.

D. Unless you want my computer to crash, insert a CD.

A. The infrastructure of our city needs upgrading, for it's in an extremely poor condition now.

B. The infrastructure of our city needs upgrading though it's in an extremely poor condition now.

C. While the infrastructure of our city needs upgrading, it's in an extremely poor condition now.

D. The infrastructure of our city needs upgrading when it's in an extremely poor condition now.

A. Researchers are developing low-cost devices that can detect water pollutants in rivers and lakes.

B. Researchers are developing low-cost devices to detect water pollutants in rivers and lakes.

C. Researchers are developing low-cost devices so that they can detect water pollutants in rivers and lakes.

D. Researchers are developing low-cost devices who can detect water pollutants in rivers and lakes.

A. While carrying out projects to develop a city, urban planners look at the needs of local people and the environment when they do this.

B. While carrying out projects to develop a city, urban planners look at the needs of local people and the environment.

C. If they carry out projects to develop a city, urban planners look at the needs of local people and the environment when they do this.

D. As carrying out projects to develop a city, urban planners look at the needs of local people and the environment.

A. Not only most Superstar City Dwellers are quite happy with their life and work but also Barbara and Mark are quite happy, too.

B. Most Superstar City Dwellers along with Barbara and Mark are quite happy with their life and work.

C. Like most Superstar City Dwellers, Barbara and Mark are quite happy with their life and work.

D. Barbara and Mark are like most Superstar City Dwellers because they are quite happy with their life and work.