OPTIONS:
[1]. body
[2]. trains
[3]. left
[4]. intermittently
[5]. down
[6]. feet
[7]. Lift
[8]. sideways

Fact 1: Gravity causes objects that have mass to be pulled down on a planet. Fact 2: And roller coasters work with gravity. Given the two facts above, roller coaster work the same as any object having mass being pulled how on a planet?
Answer:
[5].