Fill in the blanks with an appropriate Adverb.

I _____ forgot her birthday, and I just don't know how to make it up to her.

completely

The correct answer is Option (1) → completely

• The sentence "I _____ forgot her birthday, and I just don't know how to make it up to her." suggests that the speaker entirely forgot the birthday and now regrets it.
• "Completely" is an adverb of degree, which modifies "forgot" to indicate total forgetfulness.

 "I completely forgot her birthday, and I just don't know how to make it up to her."

OTHER OPTIONS

 "Always" – Means "all the time," which contradicts the context of forgetting.
  "Never" – Means "not at any time," which does not fit the idea of regret after forgetting.
  "Frequently" – Means "often," but forgetting a birthday repeatedly does not match the given context.