When a river’s water level reaches 10 metres, this means that:
(a) the water level is 10 metres above an arbitrary ‘zero’ level
(b) the water level is 10 metres above mean sea level
(c) the water level is 10 metres above mean sea level or an arbitrary 'zero' level
(d) it will flood.
(a) the water level is 10 metres above an arbitrary ‘zero’ level
(b) the water level is 10 metres above mean sea level
(c) the water level is 10 metres above mean sea level or an arbitrary 'zero' level
(d) it will flood.