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

People sails in a rocky river on inflatable individual boats. The boats pass with difficulty between the rocks. then

Available choices: - , the boats pass in the lake on the basically straight river.. - , a man wake boards on a waterfall.. - , people enters in more troubled waters.. - , a man is in a pack, going in a diving board..
The answer is:
, people enters in more troubled waters.