Read paragraph and choose the correct A, B, C or D for each questions below

Tsunamis, whose name derives from the Japanese expression for ʻhigh wave in a harbourʼ, are giant sea waves. These waves are quite different from storm surges. They are also referred to by the general public as tidal waves although they have nothing to do with tides. Scientists often refer to them as seismic sea waves, which is far more appropriate because they are often the result of undersea seismic activity.

Tsunamis can be caused when the sea floor suddenly moves, during an underwater earthquake or volcano, and the water above the moving earth is suddenly displaced. This sudden shift of water sets off a series of waves. These waves can travel great distances, at speeds close to 700 kilometres per hour. In the open ocean, tsunami waves are not very high, often no more than one or two metres. It is when they hit the shallow waters near the coast that they increase in height, possibly up to 40 metres.

The word ʻshallowʼ in the passage mostly means __________.

not deep

coastal

tidal

not clear