Conjunctions are words that are used to connect words, phrases, or clauses. They help to establish relationships between these elements in a sentence. One type of conjunction is a coordinating conjunction, which is used to connect words or groups of words that have equal importance.

The conjunction "or" is used to indicate a choice between two alternatives. It presents two options and suggests that only one of them can be chosen.

Here is an explanation of the correct answer:

Conjunctions:
- Conjunctions connect words, phrases, or clauses.
- Coordinating conjunctions connect words or groups of words that have equal importance.
- One type of coordinating conjunction is "or".

Choice between two alternatives:
- When we have two options and need to indicate a choice, we use the conjunction "or".
- This suggests that only one of the options can be chosen.

Example:
- Let's consider the sentence: "Do you want an apple or an orange?"
- In this sentence, the conjunction "or" is used to present two alternatives (apple and orange).
- The speaker is asking the listener to choose between the two options.

Usage:
- The conjunction "or" is commonly used in everyday language.
- It is used in questions, statements, and commands to present a choice between two alternatives.
- It can be used to present choices in various contexts, such as food preferences, decision-making, or problem-solving.

Other conjunctions:
- The conjunction "and" is used to connect words or groups of words that are similar or related.
- The conjunction "but" is used to connect words or groups of words that present contrasting or contradictory ideas.
- The conjunction "since" is used to indicate a reason or cause for something.

In summary, the conjunction "or" is used to indicate a choice between two alternatives. It is a coordinating conjunction that connects words or groups of words with equal importance.