Laura, 14 I've got a bike. They are not 4 way to travel, but they are good for our health.

В пропуске необходимо употребить прилагательное dangerous (опасный) в сравнительной степени. В задании дан союз than, следовательно, прилагательное употребляется в сравнительной степени.

I've got a bike. They are not as dangerous a way to travel, but they are good for our health.

Ответ: I've got a bike. They are not as dangerous a way to travel, but they are good for our health.