Answer:
A relation f(x) is a function only when there is not two different values in the range that are related to the same value in the domain.
This means that does not exist y1 and y2 such:
f(x1) = y1
f(x1) = y2
if this happens, f is not a function.
Upper graphs, from left to right.
the first graph is a constant line, this is a function f(x) = c.
The second graph is not a function.
The third graph is not a function
the fourth graph is a function
the fourth graph is a function
the fifth graph is not a function.
From the lower ones:
The set of data can be a function
y = 2x^2 - 3 is a function.
The diagram with two circles is not a function (there are more than one output for some imputs)
The last table is a function