Consider the following sentence

"It is apparent that both nations saw considerable fluctuation in population, with lows during the 1940s and highs during the 1950s."

I would like to ask when can we add comma and followed by a sentence without verb to supplement the previous sentence?

Beef has replaced chicken, becoming the most popular food.

Moreover, when can we use "ing-form" to connect two setence like the above?

Btw, in "both nations saw considerable flucuation" , the usage of saw is valid?

Thank You very much.
AnonymousI would like to ask when can we add a comma followed by a sentence without a verb to supplement the previous sentence?
There is no formula that you can follow. If you read a lot of English and try to imitate these structures when you write, you will eventually know when and when not to to these constructions in your own writing.

AnonymousBeef has replaced chicken, becoming the most popular food.
This is correct.

AnonymousBtw, in "both nations saw considerable flucuation" , the usage of saw is valid?
Yes. saw can mean experienced.

CJ
Thank you very much

But when can we make setence like the following setence? Valid when sharing same subject?

"“Beef has replaced chicken, becoming the most popular food."
Students: Are you brave enough to let our tutors analyse your pronunciation?
AnonymousValid when sharing same subject?
That is the minimum requirement, yes. Also, there must be some meaningful connection to the main clause, sometimes involving causation, sometimes involving concurrent time. Other than that, it's hard to say.

Take a look here and see if that helps.

http://grammar.about.com/od/basicsentencegrammar/a/BuildPartPhrase.htm

CJ