Question 24 is based on the passage you have just heard.

      （22）Texting while driving was listed as a major cause of road deaths among young Americans back in 2013. A recent study said that 40% of American teens claim to have been in a car when the driver used a cell phone in a way that put people in danger. 

       This sounds like a widespread decease—but it’s one that technology may now help to cure. T.J. Everts, a 20-year-old inventor, has come up with a novel solution that could easily put texting drivers on notice. 

      （23）It’s called Smart Wheel, and it is designed to fit over the steering wheel of most standard vehicles to track whether or not the driver has two hands on the wheel at all times. （24）Everts’ invention warns the drivers with a light and a sound when they hold the wheel with one hand only. But as soon as they place the other hand back on the wheel the light turns back to green and the sound stops. It also watches for what’s called “close-by hands” where both hands are close to near the top of the wheel so the driver can type with both thumbs and drive at the same time.

     （25）All the data Smart Wheel collects is also sent to a connected app, so any parents who install Smart Wheel can keep track of the teens’ driving habits. If they try to remove or damage the cover, that’s reported as well. 

24. What happened if the driver has one hand on the wheel?

解析：C。本题目为细节题。根据原文可知，当司机只有一只手在方向盘上时，装置会亮灯并发出警报声提醒司机。与C项相符。