问题
healthy,ProfessorJohnson_______cyclingasregularformofexerciseafterheretired
A:if I didn’t stop; would have stayed
B:had Istopped; would be staying
C:shouldn’t I have stopped; would stay
D:if I hadn’t stopped; would have stayed
B:had Istopped; would be staying
C:shouldn’t I have stopped; would stay
D:if I hadn’t stopped; would have stayed
正确答案是：
