A Parent Wants to Encourage Achievement Motivation and Reduce the Likelihood

A parent wants to encourage achievement motivation and reduce the likelihood that their child will be tempted to cheat as they anticipate the start of their education. Which of the following responses would be most appropriate after their child has finished a challenging puzzle?

A) "You are so smart!"
B) "Wow, you finished that way faster than anyone else!"
C) "You worked very hard to finish that puzzle!"
D) "This puzzle must have been too easy, you must need a harder one!"