(1) According to the meaning of the question, one of the 34 people is required to be the person in charge.

That is, there are C34 1=34 selection methods;

(2) According to the meaning of the problem, it is divided into four steps.

In the first, second, third and fourth steps, a student is selected from 1 class, class 2, class 3 and class 4 as the group leader respectively.

Therefore, * * * has different selection methods: N=7×8×9× 10=5040 (species).

(3) According to the meaning of the question, it is discussed in six situations.

① Choose 1 student from Class One and Class Two, with 7×8 different selection methods;

② Select 1 student from Class 1 and Class 3 respectively, and adopt 7×9 different selection methods.

③ Choose 1 student from Class One and Class Four respectively, and there are 7× 10 different ways to choose;

④ 65,438+0 students were selected from Class Two and Class Three respectively, with 8×9 different selection methods;

⑤ Choose 1 student from Class Two and Class Four, and there are 8× 10 different choices;

⑥ Choose 1 student from Class Three and Class Four, with 9× 10 different selection methods.

Therefore, * * has different selection methods: n = 7× 8+7× 9+7×10+8× 9+8×/kloc-0+9×10 = 431(species).