This would be D. (My grades un English this semester have gone up; this semester I have all As.) This is because with A., it is two separate related sentences in one sentence just with a comma. With B., it wouldn’t work because when one uses a semicolon, the sentences are supposed to be separate with the semicolon so one can’t start a sentence with because. With C., My grades is not a sentence so it couldn’t be used in the semicolon as a sentence.
