we had planned to go climbing ,but our work_______,we had to cancel our plan.A.not being finished B.not having finished C.had not been finished D.was not finished那个正解是A。帮我分析下

we had planned to go climbing ,but our work_______,we had to cancel our plan.
A.not being finished B.not having finished C.had not been finished D.was not finished
那个正解是A。帮我分析下