Referee Magazine Practice Question

[McMac]

On the Referee site, they have 20 practice questions. #16 reads as follows:

Fourth and 10 from team K’s 20 yardline. K1 and K2 are positioned in front of punter K3. At the snap, nose guard R4 charges through the line, approaches K1 and K2 and leaps in an attempt to block the punt.
a. No problem under any circumstance.
b. Foul under any circumstance.
c. Foul only if R4 leaps directly over K1 or K2.

According to the answer key for NFHS, the say the answer is A. I contend that the answer is c as it would constitute hurdling which is illegal.

If I am wrong in my thinking, please explain.
Thank you!