1. Convex quadrilateral $A E C D$ has sides that are all prime numbers, and $A B /$ $C D, A B+B C=A L^{\prime}+C D=20, A B=B C$. Then $B C+$ $A D=$ ( ).
(A) 6 to 14
(B) 6
(C) 14
(D) 10
-1. (A).
Assume $A B C D$ is not a parallelogram, and $C D B C$ as well as $A B, B C$ are all prime numbers, then we can only have $B C=3$ or 7. Therefore, $A D=3$ or 7, which means $A D+B C=6$ or 14.