What does statement D(0.5) D(1) - D(0.5) mean

Question 15 of 25 2 points read the following excerpt from a speech: it has been suggested that all automobiles be converted to electric power by the year 2020. _ there simply isn't the infrastructure in place to accommodate such a change. which word or phrase best connects the ideas in these sentences? o a. nowadays o b. therefore o c. in contrast o d. unfortunately