12. Given $|a-b|=5,|b-c|=8,|c-d|=10$, then the minimum value of $|a-d|$ is ( ).
(A) 0 .
(B) 1 .
(C) 2 .
(D) 3 .
Answer: D
Solution: Since $|a-d|=|(a-b)+(b-c)+(c-d)|=| \pm 5 \pm 8 \pm 10|$,

the minimum value is $|5+8-10|=3$.

Therefore, the answer is D.