What is likely true about seeing Mary last night?

The option indicating that you couldn't have seen Mary aligns with the implication that there are strong reasons or circumstances which would prevent you from having done so. This suggests a definitive conclusion regarding your interaction with Mary, implying that seeing her was not possible based on specific conditions or knowledge.

In contrast, the other options express varying degrees of possibility or expectation related to seeing Mary. The first implies certainty, the third allows for some uncertainty, and the fourth suggests an expectation of having seen her. However, none of these options convey the definitive negation present in the correct choice, which makes it unequivocal in stating the impossibility of your seeing Mary last night. Each of these alternative possibilities lacks the strength of the finality that characterizes the assertion in the selected answer.