What potential issue can arise from wearing ordinary glasses while riding?

Answer: B — They may shatter or fall

Wearing ordinary glasses while riding can lead to safety concerns primarily because they may shatter or fall off during a ride. This can create a hazardous situation as broken pieces can cause injury to the eyes, and if the glasses fall off, it can impair the rider’s ability to see clearly. While the other options present valid concerns—fogging can obscure vision, and aesthetic preferences can affect a rider's choice of gear—these do not pose the same serious risk to safety that the possibility of shattering or losing glasses does. Additionally, while ordinary glasses might affect peripheral vision compared to specific motorcycle eyewear, the more pressing issue in an active riding scenario is the risk of breakage or loss, which is critical for maintaining visibility and control while riding.