4. At a large conference, four people need to be selected from five volunteers, Xiao Zhang, Xiao Zhao, Xiao Li, Xiao Luo, and Xiao Wang, to undertake four different tasks: translation, tour guiding, etiquette, and driving. If Xiao Zhang and Xiao Zhao can only perform the first two tasks, and the other three can perform all four tasks, then the number of different selection schemes is. kinds.
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