Find the synonym of the underlined word.
The musicians who graduated from that school are adept at playing at least four instruments.
a. Proficient
b. Adjustable
c. Awkward
d. Careful
e. Proverbial

Hint: If a word is equal in meaning to another word, it is said to be the synonym of that word. For example, the synonym of peaceful is quiet.

Complete answer:
 Let us look at the word ‘adept’ in the given sentence. Adept means, to be skilled at something. For example, he was adept in his job. It means that he was skilled in his job, that is, he did his job well. Now, proficient also means to be good at something. So, this word proficient fits well in the given sentence. The musicians who graduated from that school are adept / proficient / were good at playing at least four instruments. Thus, option a is the correct answer.
Option b, adjustable, means to be able to be adjusted. Adjust means, to alter or change something in order to get a desired position or appearance. Adjusted is the past tense of adjust. For example, backpacks usually have fully adjustable straps. So, adjustable is a totally wrong option for the given sentence.
Option c, awkward, mean to be weird or uneasy. For example, she was in an awkward position when her dad caught her partying late at night. As is obvious, this option is also wrong.

Option d, careful, means to be cautious or alert. I was careful while writing these answers. That means I was cautious while writing - I did not want to make any mistake or leave loopholes in my answer. In the given sentence, it is not the correct option.

Option e, is proverbial. It stands for something well-known or commonly used, or a part of a proverb. Suppose you are giving the same excuse over and over again for not doing your homework, I can tell you, “Stop giving those proverbial excuses.“

Note: Put the words in the options in place of the underlined word in the sentence and check if they leave the meaning of the sentence unchanged. Only then will it be easy to get the correct option.