The correct option is C
A is not true because standard is the cheapes in the period 5 to 10 months, we can see this because the two other lines are above the line of standard in this period, thus standard is the cheapest in the interval
B is not true because monthly becomes more expensive than standard at month 5.
D is not true because monthly is the cheapest fom month 0 to 5.
Then, the only option is true, over the first 5 months, monthly is the cheapest
