Concept:The idiom "cry over spilt milk" means to waste time feeling regret about something that has already happened and cannot be changed. Explanation:This phrase warns against uselessly lamenting past mistakes or losses. Instead of moving forward, a person dwells on what is already done. The correct option "Regret a past loss" directly captures this meaning. For example, if you break a vase, crying about it does not fix the vase. It is better to accept the loss and focus on the future. The other options do not fit. "Ignore problems" means to deliberately avoid issues. "Be indifferent" means to show no emotion or concern. "Work harder" means to put in more effort. None of these describe regretting an unchangeable past event. Therefore, the idiom matches "Regret a past loss." Answer:Option A: Regret a past loss.