The two sentences that best support the inference that Mr. Denis does not know Janet is training for the "Mud and Sweat" race are:
Mr. Denis noticed that Janet's attitude had changed; she was training hard at practice and she seemed to be enjoying herself.
He wasn't sure what had transpired, but he was glad to see Janet happier and more determined to improve.
<h3>What is an Inference?</h3>
An inference is a deduction based on facts. In the story given, we can deduce that Mr. Denis did not know Janet's intention for training hard from the sentences above.
These sentences indicate that Mr. Denis was happy about the improvement on Janet's part but could not fathom why there was this sudden improvement.