Based on what we know about the Unification of 1861, the correct statement is that The new nation included much of mainland Italy and several islands.
Before the unification, there were several states in Italy such as Tuscany, Venetia, the Papal States, and the Kingdom of Sardinia. Most of these states joined together in 1861 to make the unified kingdom of Sardinia.
In conclusion, option D is correct.
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