Mark the letter A, B, C, or D on your answer sheet to indicate the sentence that best combines each pair of sentences in the following questions.
Alternative sources of energy have environmental advantages. It’s not easy to make full use of them.
A. Because alternative sources of energy have environmental advantages, it’s not easy to make full use of them.
B. Alternative sources of energy have environmental advantages, so it’s not easy to make full use of them.
C. Despite their environmental advantages, it’s not easy to make full use of alternative sources of energy.
D. Although alternative sources of energy have environmental advantages, but it’s not easy to make full use of them.