Question

Colloquial English is:

A- the language of technical reports
B- a regional variation of English
C- conversational idiom
D the language of educated Americans

Answer 1

Colloquial English is a collection of ways that we say something, that is not meant to be taken literally (including Idioms). It is informal speech.

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Here are a few examples:

1. He's going to be in hot water.

--It ACTUALLY means, "He's going to be in trouble," not "hot water." It doesn't mean that he's going to LITERALLY BE IN HOT WATER.

2. My child is burning up.

--It ACTUALLY means, "My child has a fever." It doesn't really mean that the child is LITERALLY BURNING UP IN FLAMES, you see?

3. She was caught red-handed!

--It ACTUALLY means, "She was caught in the act!" It doesn't really mean that her hand was LITERALLY RED.

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Colloquial English is where we say something that is NOT meant to be taken LITERALLY, you see?

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Now, I'm having trouble deciding which of your choices is correct. The way I see it, it could be.....

B. Because different parts of America, and different English-speaking countries all have their own forms of Colloquial English.

or

C. Because much of colloquial English IS conversational idioms.

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In the end, I would lean on B.

Because more and more "conversational idioms" are becoming a part of formal writing nowadays. So it might not actually be C.

Answer 2

Everything you say is true, but in your final choice, you are making things too complicated.
In a simple question like this one, the expected answer is certainly C