i agree driving on trail and trail cycling are different. driving can include 4x4 atvs etc. but option is saying trail cycling which = mountain biking i think
C
A. Mountain biking on trails is getting popular. - It is the conclusion
B. stores are selling more mountain bikes and mountain bikes are a greater proportion of their overall bike sales. - It is not what is being the main point. It is the effect.
C. The people who are buying bikes must be using them on trails. - By applying the negation technique, we will get nil motivation to buy the bikes. eg it hurts the most and hence it is the correct answer.
D. Most of the people who are driving the increase in mountain bike sales are involved in trail cycling. - New information./ Shell answer: driving on trail and trail cycling are different.
E. People who buy mountain bikes tend to use them in urban or suburban settings, rather than on trails. - New information.