12 The number of arithmetic sequences that satisfy the first term is 1783, the last term is 1993, the number of terms is no less than 3, and the common difference is a natural number greater than 2 is
A. 12
B. 13
C. 14
D. 15
12 B. From $(n-1) d=a_{n}-a_{1}=210=2 \times 3 \times 5 \times 7$, and $n \geqslant 3, d>2(d \in \mathbf{N})$, we know that $n-1$ can be $2,3,5,7,6,10,14,15,21,30,35,42,70$, a total of 13 values. Therefore, there are 13 arithmetic sequences that satisfy the conditions.