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.