Which option best explains the meaning of the idiom "the alpha and the omega" as it is used in English?

Introduction / Context:
The idiom "the alpha and the omega" comes from the first and last letters of the Greek alphabet. It appears in religious, philosophical, and literary contexts, and it is also tested in competitive English exams. Knowing its meaning helps you understand passages that talk about completeness, totality, or something that covers everything from start to finish.

Given Data / Assumptions:
- Idiom: "the alpha and the omega".
- Options suggest different possible meanings, such as beginning and end, beauty, stars, cost, or leadership.
- We must choose the option that correctly represents the established meaning of this fixed expression.

Concept / Approach:
"Alpha" is the first letter of the Greek alphabet and "Omega" is the last. In many religious texts and later English usage, the phrase "alpha and omega" symbolises the first and the last, or by extension, the beginning and the end. It can also imply that something is all-encompassing or complete. Therefore, the option that explicitly mentions "the beginning and the end" is the correct one.

Step-by-Step Solution:
Step 1: Recall or note that alphabets, including Greek, have a first and last letter; Alpha corresponds to A and Omega to something like Z in English.
Step 2: Understand that using both letters together symbolises the entire range from start to finish.
Step 3: Among the options, only option a directly expresses this idea: "The beginning and the end".
Step 4: Confirm that other options like "a nice act" or "very costly" are unrelated to letters, alphabets, or completeness.

Verification / Alternative check:
Look at how the idiom is used in context: "For him, work is the alpha and the omega of life" means work is everything, from start to finish, central to his existence. Similarly, in religious language, describing a deity as "the alpha and the omega" indicates being present at the beginning and the end of all things. In all such usages, the notion of first and last, or totality, is clearly present.

Why Other Options Are Wrong:
- A nice act: refers to a kind or pleasant action with no connection to alphabets or completeness.

- The stars and the moon: focuses on heavenly bodies, not on beginning and end.
- Very costly: talks about price, which is not part of the idiom's meaning.
- A powerful leader: while sometimes important people are described in grand terms, this idiom is not specifically used for leaders; it is about start and finish or completeness.

Common Pitfalls:
Because the phrase sounds poetic, some learners attach random positive meanings to it, such as "very important" or "beautiful". Always remember its origin in the Greek alphabet to stay grounded in the correct meaning. Linking the idiom to the idea of "from A to Z" in English can also help you recall that it means the beginning and the end.

Final Answer:
"The alpha and the omega" means "the beginning and the end".