(1) Using the digits $1$, $2$, and $3$ to form a four-digit number, it is required that all three digits appear, and the same digit does not appear adjacent, the total number of such four-digit numbers is ( ).
(A) 24
(B) 18
(C) 15
(D) 12
1 B Prompt: From the problem, we know that one of the numbers $1, 2, 3$ must be used repeatedly. There are 3 scenarios; placing 2 identical numbers in two non-adjacent positions of the four-digit number, there are also 3 scenarios; placing the remaining 2 numbers in the remaining 2 positions of the four-digit number, there are 2 scenarios. Therefore, a total of $3 \times 3 \times 2=18$ different four-digit numbers can be formed.