The correct option is B (II, III and I).
Savoy Sardinia (1858–60) joined first, followed by the Kingdom of the Two Sicilies (1860), and Venetia joined last in 1866.
The map in Fig. 14(b) of the textbook clearly shows the years each region joined unified Italy: Sardinia-Piedmont/Savoy Sardinia was the base state (1858–60), Garibaldi won the Kingdom of the Two Sicilies in 1860, and Venetia was added in 1866. Students should memorise these dates from the unification map.