Read the text and complete it with the best word that fits each gap. Use only one word in each gap

Journey Deep into the Earth

In 1991, a local farmer in Vietnam found a cave deep in the Vietnamese jungle. Little [ ] a team of British cave explorers know what awaited [ ] as they followed the farmer into the cave years later in 2009. They [ ] about to discover the world's largest cave measuring approximately 9 kilometres long and 150 metres high with a river running [ ] it. The cave, called Son Doong, was created some 2 to 5 million years [ ] by river water eroding away limestone underneath a mountain. Some parts [ ] the cave's roof have collapsed creating huge skylights. As a [ ] of these skylights, vegetation began to grow and formed the largest underground jungle. According [ ] explorer and photographer Carsten Peter, [ ] spent weeks inside the cave, the Son Doong cave is by [ ] the largest and most unique cave ever discovered. It is [ ] large that explorers are still searching [ ] its end!