What is the recommended length for the nails used in the joints of the reinforcement boards with the uprights in the butt joints?

I - The joints of the four reinforcement boards with the uprights in the butt joints must be fixed at each end with three nails of 75 mm (≈ 3") or more in length.
II - The joints of each board with the stops must be fixed with two nails of 63 mm (≈ 2 1/2") or more in length.
III - The joints of each board with the platform reinforcements and with other boards must be fixed with two nails of 100 mm (≈ 4") or more in length.
a) Only I is correct.
b) Only II is correct.
c) Only III is correct.
d) I, II, and III are correct.