Which of the following is a complex sentence? a. the fence may deter immigration in some areas, but many are concerned about its impact on the natural environment. b. many believe that the border fence will impact illegal immigration rates; however, environmental groups are very concerned about how it will affect wildlife and nature. c. there is political support for the border fence. there are also concerns about its effects on wildlife and nature. d. a border fence may deter immigration. but many are concerned about how it might impact wildlife and the natural environment.