I won’t tell the student the ans

I won’t tell the student the answer to the math problem until he ___ on it for more than an hour.
A、has been working
B、will have worked
C、will have been working
D、had worked
【正确答案】：A
【题目解析】：我不会告诉学生数学问题的答案，直到他思考了一个多小时的时间。