Answer:
D. You purchase a watch for your mom's birthday, and then discover she just purchased the same watch for herself online.
Step-by-step explanation:
Situational irony occurs when the character did an action expecting a result, but the result that happens is different from what the character expected. In this case, you did an action that was to buy a watch and wanted to give it to your mother since she did not have that watch, but something different happened; your mother had already bought an equal watch.