WE/ SURVIVE/ START/ WORK/ CLEANER/ SAFER/ SOURCES OF ENERGY//A. WE...

54. We/ survive/ start/ work/ cleaner/ safer/ sources of energy//

a. We won’t survive unless we start working on cleaner, safer sources of energy.

b. We won’t survive if we start working on cleaner, safer sources of energy.

c. We will survive if we start work on cleaner, safer sources of energy.

d. We will survive unless we start working on cleaner, safer sources of energy.