How is a monologue different from a formal speech or soliloquy?
a) A monologue is given when a character is speaking to himself or herself, the other two are directed at another character
b) A monologue is given when a character is speaking to another character, the other two are not
c) A monologue and soliloquy are the same things, but a formal speech is given to an audience
d) All three are just different names for the same thing

Hint:A monologue and soliloquy are types of dialogue of theatre art, while speech is a way of mass communication directed towards the audience.

Complete answer:
 A monologue and soliloquy are two different literary terms, and speech is a vocal form of communication. This makes option d ‘All three are just different names for the same thing’ invalid.’ Irrelevant.
Monologue and soliloquy do have something in common, i.e. they are both delivered by individual speakers but, they are not entirely the same. A monologue refers to a literary device used in drama, theatre, and literature which is characterized by a long speech delivered or presented by an individual character. It is delivered to the other characters of the play or to the audience. A soliloquy is also a long speech delivered/ presented by an individual character but, it is not aimed at the audience. This is a speech that one gives to oneself. It is like thinking out loud, this helps the audience to understand what is going on with the character internally. Speech is an expression of thoughts in words to the audience. A monologue and soliloquy is a type of literary speech, but a speech, in general, is formal. As per the information that we have option b, ‘A monologue is given when a character is speaking to another character, the other two are not’ is the most appropriate answer.
Option ‘a’ is incorrect as a speech and soliloquy is not directed to other characters.
Option ‘c’ is incorrect as a monologue and soliloquy are not the same.

Note:
The similarity monologue and soliloquy share i.e. both are delivered by a single speaker, do not make the same. Also, both being a type of literary speech as mentioned above does not make them same as speech.