Mark the letter A, B, C, or D to indicate the sentence that best combines each pair of sentences in the following questions.
We have been trying to learn English for years. We haven't succeeded yet.
A. Although we have been trying to learn English for years, we haven't succeeded yet.
B. After we've been trying to learn English for years, we have succeeded.
C. We haven't succeeded yet since we have been trying to learn English for years.
D. We have been trying to learn English for years, so we haven't succeeded yet.
