challenge: Why have courts been slow to issue clear guidance on the issue of whether the use of trademarks as keywords constitutes trademark infringement?
  
  A. Because the majority of keyword advertising cases are settled out of court and do not proceed to trial
  B. Due to a lack of trademark infringement cases being brought to court
  C. As a result of a lack of understanding of pay-per-click advertising
  D. Due to the complexity of trademark laws
  Answer: 