Final answer:
The old woman secures marriage to the knight by having Option 3: him pledge to grant her first request, which she later reveals to be his hand in marriage.
Step-by-step explanation:
The old woman in question gets the knight to marry her by making Option 3: him pledge to honor her first request. This tactic aligns with Option 3 from the given choices.
The knight agrees to this condition without knowing what her request will be. Eventually, when the time comes for the old woman to make her request, she asks the knight to marry her, a request he is obliged to fulfill since he pledged his honor.
This form of obtaining marriage through a pledged promise is indicative of medieval narratives where characters often find themselves bound by their word, demonstrating the high value placed on honor and vows during this period.