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.
I suppose they are very tired. They have been working all morning.
A.Because they have been working hard they are now very tired.
B.They must be very tired as they have been working all morning.
C.They can be very tired due to working all moming.
D.They were very tired because of a hard working moming.