Which of the Following Statements About Factors Affecting Conditional Reasoning

Which of the following statements about factors affecting conditional reasoning is correct?

A) The length of a problem is more important in determining problem difficulty than is the abstractness of the problem.
B) People typically make more errors with abstract problems than with concrete problems.
C) People have more difficulty with sentences containing a single negative than they have with double-negative sentences.
D) If a problem contains the word not in the antecedent, people have difficulty; however, the word not in the consequent does not influence response speed.