Read the sentence from Alexander’s paper.

When asked if she was loyal enough to become a secret agent, Keysha answered in the affirmative.

In which revised sentence did Alexander change the underlined word to use it as an noun?

Since she was affirmably loyal, Keysha was able to become a secret agent.
Before becoming a secret agent, Keysha needed to affirm her loyalty.
As an affirmation of her loyalty, Keysha agreed to become a secret agent.
Once she finally affirmed her loyalty, Keysha became a secret agent.