Answer: The correct one is C
Step-by-step explanation:
The gaussian curve ( the one you can see in the graph) is described by C.
You can see that A is an exponential function that only will grow as t grows.
B will decrease asymptotically to zero as t grows, the same with D, as t grows, D only can decrease.
but for C you will have the maximum when x = b, and a exponential decrease when x decrease or when x increase which forms the bell that you see in the graph.