A is the answer. Because every time you half a fraction, it's like timesing the denominator by 2. So like a half into a quarter, and a quarter into eighths.
As for your question. You keep on halving your fraction until you have done it seven times.
I think I've done it correctly and I got 1/256, but I didn't really have a calculator with me. If you are doubtful, I suggest just checking if it's right with a calculator