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What is the difference between "is" and "is being"?
For example:
McCain pizza is being sold for 4.99 at the grocery store.
McCain pizza is sold for 4.99 at the grocery store.
Comments  
"is being" implies that it's a temporary condition. Perhaps it's on sale right now, and it will return to a higher price next week.
The workers are building a new road.

The road is being built by some workers.

Sometimes the words 'is being something' stand for passive construction too.
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It's the difference between a trait and a state.

is
= is always; is typically; is usually; is characteristically (trait)
is being = is at the moment; is now; is for a limited time now; is currently acting as; is in this instance (state)

George is a pain in the neck.
George is being a pain in the neck.

The teacher is rough on his students.
The teacher is being rough on his students.

Christy is a fool.
Christy is being a fool.


CJ
CalifJim
I hope you recognize me. I admire your standard of English. I posted questions, in the past, using different names. You gave me some excellent answers.

George is a pain in the neck.
What does this mean? I don't understand.
You could say 'George has a pain in the neck'.
Yes, nice to "see" you again, Rex! Emotion: smile

When someone is "a pain in the neck", they are a nuisance. They bother you. They are annoying and troublesome. They make your life miserable with their behavior.

(In this idiom, people often substitute other words for "neck", particularly words that indicate the part of the body you sit on. Emotion: smile)

CJ
Students: We have free audio pronunciation exercises.
CalifJim
I am glad you recognize me. I didn't know those words. I just looked up it in online Cambridge dictionary.

It is informal. For me, informal means either slang or rather confine to BrE or AmE.
I may be wrong.
[Those days I used to write '' I maybe wrong'. You corrected my mistake. Now I always write 'may be'. You helped to correct my mistake more than a year ago.]
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a pain (in the neck) INFORMAL
someone or something that is very annoying:
That child is a real pain in the neck.
You explained in simple way. Thank you sir