25

Sand dunes are rarely isolated. It’s ………………… for a dune to stand alone. They form in large groups known as dune fields.

COMMON

26

It’s well-known that sand dunes move around and that smaller dunes move faster than larger ones. Now ………………… have discovered that dunes communicate with their neighbours. They can even push their neighbour dunes farther away.

RESEARCH

27

Here’s what’s happening. A flow of water or wind hits a dune. The energy creates a disturbance. The disturbance gives the ………………… dune a little push. This causes that dune to move faster.

NEIGHBOUR

28

As the flow continues, the movement continues. Finally, a dune is far enough away not to be affected by the disturbance. What is more, scientists thought that a pair of identical dunes would move together at the same speed. Instead, ………………… enough, they push away from each other.

AMAZING

29

So, some dunes move closer to roads and infrastructure. Some cover parts of cities, destroying people’s livelihoods. Now we know, they communicate, but do they ………………… ?

APOLOGY