I am practising and doing exercise on the differences between simple past and present perfect. One of the rules I've learnt states that present perfect should be used when an action happened in the past but at a nonspecific moment of time. So when we do not know exactly when it happened.
My question regards the application of this rule in this text I posted, sentence number 6. I would have completed it with "have bought", but in the book I find that the right answer should be "bought". Why is that?
Thanks for your help!