Since g(x) is a positive function (the values are positive for all x), the options A. and B. are not correct, because -3^x is a negative number bigger than +2 or -2 for some values of x.
Then, in order to check for C. and D., let's find the value of g(x) in each case for x = 0:
C.
D.
Looking at the graph, for x = 0 we have g(0) = 3, therefore the correct option is C.