This is a test of commonsense with single/multi-choices. Complete the next sentence:

Several people are riding horses in an outdoor arena. they

OPT: a. are involved in a game of polo.. b. are tied onto ropes and jumping up and down.. c. are lined up in a border drawn.. d. come in a large arena and take off through jumps and ropes and into the sand..
The answer is:
a.