Correct Answer: Grit

Solution : The correct choice is the first option.

Fortitude refers to courage, strength of mind, and resilience in the face of adversity or challenges.

Grit: This word shares a similar meaning with "fortitude". Grit is the courage and resolve to persevere and overcome obstacles.

The meanings of the other options are as follows:

• Vacillation: This means indecision or wavering, which is the opposite of fortitude.
• Plot: This refers to a secret plan or a storyline, not synonymous with fortitude.
• Grim: This describes something stern, forbidding, or unrelenting but doesn't capture the full sense of courage and resilience embodied in fortitude.

Therefore, the correct synonym of the given word is grit.