What does the left y-axis show?
a- sea surface temperature anomaly, in degrees celsius
b- sea surface temperature anomaly, in degrees fahrenheit
c- time, in four-year intervals
d- incidence of cholera, as a percentage of the normal rate
e- sea surface temperature, in degrees celsius

The correct option is;

a- sea surface temperature anomaly, in degrees Celsius

Explanation:

From the diagram related to the question we have two graphs super imposed of Sea surface temperature anomaly, in degrees Celsius and cholera incidence anomaly (%) both plotted against time in years.

On the left the y-axis represents the sea surface temperature anomaly while on the right, the y-axis represents the cholera incidence anomaly (%).

The display of the graph shows the sea surface temperature anomaly in blue.

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