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

Question. Most Superstar City Dwellers are quite happy with their life and work. Barbara and Mark are quite happy, too.

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. 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. 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. 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. For there is shortage of fresh water, wastewater is treated and turned into drinking water.

B. Wastewater is treated and turned into drinking water because there is shortage of fresh water.

C. Wastewater is treated and turned into drinking water though there is no shortage of fresh water.

D. To ensure there is no shortage of fresh water, wastewater is treated and turned into drinking water.

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.