阅读下面材料，在空白处填入适当的内容（不多于3个单词）或括号内单词的正确形式。
Imagine falling towards the planet Earth at          awesome speed of 300 kilometers per hour. You start your fall from over four kilometers above the Earth. And you have less than one minute before you pull your parachute (降落伞）cord. You are falling       fast that just turning your head can send you off       a different direction. This is the wild side of a sport that has not found its limit—freeflying.
Freeflying       (base) on the more traditional skydiving,      of which are eye-catching. However, it is more terrifying to watch freeflyers create formations and movements. Freeflyers,       the name suggests, enjoy the more spontaneous(即兴的）thrill of doing their own things.
The wildest trip for a freeflyers is falling ‘head down’. Falling ‘head first’ requires a great deal of control, which means          (travel) not only fast but also steadily. Even the    (slight) movement has a great effect on your direction.
They wear the amusing jumpsuits, strange helmets and smaller parachutes.      (actual), their parachutes are about one quarter the size of the traditional skydiver’s parachutes. It is only in the last few years        freeflying has gained any real public acceptance.