PT 30 S2 Q9

A running track with a hard surface makes for greater running speed than ... ...

Which one of the following, if true, is evidence that the explanation given above is only a partial one?
(A) Dry running conditions can be guaranteed for indoor track races only.
(B) ...
(C) ...
(D) ...
(E) ...

*This question is included in Practice Set: "Weaker" Questions, Set 3 - Difficult/Uncommon Mix (25Q)