Strong root systems and long flexible stems allow plants to survive in the strong currents of which ecosystem

The Aquatic ecosystem.

Explanation:

The long (usually thing) stems allow the plants to not resist the overbearing underwater currents of the ocean ecosystem. The roots need to be strong so that flexibility can be established during stronger currents as well as anchorage to keep the plants attached to the ocean bed (or other surface) in order to survive and flourish. Some plants even have air bubbles within them to allow them to be able to float and stay upright in the water.

Their stems can be long and flexible because most aquatic plants don't have a water tissue transportation system within their stems but they rather directly consumed the needed minerals and vitamins from surrounding water while they are submerged.

whichever one it is, it's definitely not one that you included on the list you provided.

the first american roller coaster was the mauch chunk switchback railway, built in the mountains of pennsylvania in the mid-1800s. the track, originally built to send coal to a railway, was reconfigured as a "scenic tour."