The choices can be found elsewhere and as follows:
A)The reaction requires the collision of three particles with the correct energy and orientation.
B) All reactions that occur in one step are slow.
C)The probability of an effective three-particle collision is low.
D) The transition state is low in energy.
I think the correct answer from the choices listed above is option C. If the uncatalyzed reaction occurs in a single elementary step, it is a slow reaction because the probability of an effective three-particle collision is low.