Read the following text and choose the best answer.
Which statement is NOT true about Son Doong Cave?
A. Tourists can explore Son Doong Cave daily throughout the year.
B. The cave was formed about 2 to 5 million years ago.
C. It was formed by river water eroding away the limestone underneath the mountain.
D. Some of the stalagmites in Son Doong Cave are about 70 metres tall.