10. A person needs to climb 10 steps to go from the first floor to the second floor. He can take one step at a time, called a one-step, or two steps at a time, called a two-step, or three steps at a time, called a three-step. He takes a total of 6 steps to go from the first floor to the second floor, and no two consecutive steps are three-steps. Then the number of different ways he can go from the first floor to the second floor is ( ).
(A) 6
(B) 8
(C) 10
(D) 12
10. C.

According to the requirements of the problem, it is not difficult to verify that among these 6 steps, there cannot be no third-order steps, nor can there be more than 1 second-order step. Therefore, it can only be 1 third-order step, 2 second-order steps, and 3 first-order steps.

For the sake of vividness, we can use white, black, and red balls to record the process of crossing 10 steps from the first floor to the second floor:

White balls represent first-order steps, black balls represent second-order steps, and red balls represent third-order steps. Each process can be represented by a permutation of 3 white balls, 2 black balls, and 1 red ball, where balls of the same color are not adjacent.
We will discuss this in three scenarios.
(1) The 1st and 6th balls are both white, then the two black balls must be on either side of the middle white ball. In this case, there are 4 spaces between the black and white balls to place the red ball. Therefore, there are 4 different possible arrangements in this situation.
(2) The 1st ball is not white.
(i) If the 1st ball is red, then the remaining 5 balls have only one possible arrangement;
(ii) If the 1st ball is black, then the remaining 5 balls have two different arrangements due to the different positions of the red and black balls. This scenario has a total of 3 different arrangements.
(3) The 6th ball is not white, the same as (2), there are a total of 3 different arrangements.

In summary, according to the requirements of the problem, there are $4+3+3=10$ different possible processes from the first floor to the second floor.