请选择ABCD2E-w2l7|6I'I-|:p2^*r I haven’t heard from Bill _______ he left here.7N.p;E-L;|'v7~2y7l
A. when7N.p;E-L;|'v7~2y7l
B. before7N.p;E-L;|'v7~2y7l
C. since7N.p;E-L;|'v7~2y7l
D. while7N.p;E-L;|'v7~2y7l