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

Several people are floating on tubes down a river. they

Select from the following. (i) all look like they are in a tube going down a hill.; (ii) pull themselves through the water.; (iii) move in unison on the water water.; (iv) lay back in the tubes, riding the waves as they go.;
The answer is:
(iv)