No matter how hard he tried, Mike could not make sense of his economics textbook.
A. Mike could not understand his economics textbook because he hardly tried to at all.
B. In spite of his efforts, Mike was unable to understand the contents of his economics textbook.
C. If Mike had studied harder, he would have been able to comprehend what was in his economics textbook.
D. It was impossible for Mike to understand his economics textbook without making a great effort.