Answer:
D is correct graph.
Step-by-step explanation:
A 100-gallon fish tank fills at a rate of x gallons per minute.

If the tank has filling for 20 minutes, The total time to fill the tank is represented by the function,

It is rational function. We need to draw the graph of this function.
First we find vertical asymptote.
For VA: x+20=0
x=-20
For x-intercept, Put f(x)=0

No x-intercept
For y-intercept, Put x=0
y-intercept: (0,5)
For HA, 
y=0
Please see the attachment for graph.
Hence, D is correct graph.