Correct Answer: To allow a secret to be known, usually without intending to.

Solution : The correct option is the third option.

Explanation:
The idiom let the cat out of the bag means to allow a secret to be known , usually without intending to. In this context, it implies that the MD unintentionally revealed the secret about the promotion.

The meanings of the other options are as follows:

• Openly confess means admitting something openly, not necessarily related to revealing a secret.
• Creating a false story means making up a story that is not true and unrelated to the unintentional revelation of a secret.
• Secretly confide means sharing a secret in a confidential manner, which is different from unintentionally letting a secret slip out.