Final answer:
The correct match for "unnerve" is 'upset,' as it means to disturb someone's confidence or composure. Option a.
Step-by-step explanation:
The word "unnerve" means to make someone lose courage or confidence, to upset or disturb their composure. It does not mean to cheer, organize, or measure someone or something. Therefore, the correct match for "unnerve" from the given options is upset.
To understand more clearly, consider the origin of the word "unnerve". It comes from the prefix 'un-' meaning 'not,' combined with 'nerve,' which refers to strength or steadiness. So, 'unnerve' originally meant to deprive of nerve or strength, hence making someone disturbed or disappointed in their abilities.
It is important to note that "unnerve" is not associated with positive connotations such as cheering someone up, nor does it deal with tasks such as organizing or measuring, which are systematic and orderly actions. Instead, it involves an emotional response where a person's inner confidence or stamina is disturbed.
So option a.