Помогите с заданием по английскому, срочно!!

Read the text, and write the correct word in gap 9 to complete the text. Use only one word for the gap.
Wheelies, half-shoes, and half-roller skates (9) have quickly become popular in schools up and down the UK. The shoes (10) have a wheel at the back, allowing kids to go from walking to rolling simply by moving their weight to the back of their foot. But Wheelies aren't popular with everybody. There have (11) been a lot of accidents and the shoes (12) will be particularly dangerous if kids have never used them (13) Steve Jones, (14) owns a shoe shop, says, 'These shoes might (15) be dangerous in some situations, but after about two hours most kids (16) find it easy to control them.' Steve (17) is starting 'Wheelie Classes' next month, which he hopes will help children avoid accidents in the future.