Why is the answer b? The shop is closing soon, so they should hurry up to get to the shop, so isn't d the answer?
W:Mike, what will you buy Sara?
M:I've narrowed it down to a necklace or a brooch
W:You should hurry up. The shop is about to close.
M:______b________
a.Yeah, She'll like them
b. Maybe I'll just buy both.
c. I'd say in a few minutes
d.We can arrive quickly.
Good question.
My feeling is that the two speakers are already inside of the store when the conversation takes place. That makes "b" the correct answer. If they were outside, on their way to the store to buy a gift, "W" (in line 3) would have said "We should hurry". That would give some support to answer "d".
However, it is not clear at all and this question isn't very well constructed.