I know I (supposed, phone) you yesterday, but I've lost my mobile! I'm sure I hsd it with me when I left work, so I (can't, leave) it on my desk. I suppose I (might, drop) it on my way out or it (may, fall) out of my pocket on the train. or I suppose someone (could, steal) it! what(coul, happen) to it? I dropped it, someone (should, find) it by now.

Was supposed to, couldn't have left, might have dropped, may have fallen, could have stolen it, could happen, should have found.