Omission of to be verbs in Passive sentences

Your second sentence does not lack a verb form, it lacks a pronoun. Specifically, the interrogative pronoun "who"--Researches have found that people who are exposed to intense sunlight may harm their skin. In both sentences, you need to get rid of the comma after the word "that."

Ok, here is my doubt. First, I thought exposed was an adjectival participle. But now, based on this article (http://en.wikipedia.org/wiki/Adjective_phrase), I think the whole thing is an attributive adjective phrase in both sentences. Neither sentence is in the passive voice. Both phrases answer the question "which people?"

Researches have found that people (exposed to intense sunlight) may harm their skin.

Researches have found that people (who are exposed to intense sunlight) may harm their skin.

Any thoughts?

let me bring another example.
Effects caused by the air pollution are underestimated.
Effects, which have been caused by the air pollution are underestimated.
"have been" has been omitted in the second sentence. Why? When we are allowed to do so?(always)

I have no idea what you think you are saying. To dispense with this at the outset, you do not use a definite article in such a construction. It is "air pollution," not "the air pollution."

Why do you say "have been" has been omitted in the second sentence? It is clearly there. You're not making any sense.

Hi Dear,
I thought that you are enough intelligent to find my mistake. (in the first sentence "have been".....)

Apparently, i'm not. It's not needed in the first sentence . . . Dear.

Thank you so much.

You're welcome. I hope it is clear to you now.

Neither clause is in the passive voice. The passive voice requires the verb "to be" plus the participle of another verb: was sold, were created, am told, etc.



This sentence is correct and the phrase in parenthesis is an adjectival phrase of some sort (what effects?). Since it is a dependent clause (does not make sense on its own), it does not require a comma.



This sentence is wrong. Since "which have been caused by air pollution" is a dependent clause, the comma should not be there. "Have been" is part of the adjectival phrase but can be omitted.

I am a student of grammar, so if I am wrong, someone else please let me know.

Saying that a sentence is wrong because of the placement of punctuation is a dubious proposition. While the placement of punctuation may change the meaning of a sentence, it is a separate issue from the grammar.

Thanks Setanta. I thought punctuation was part of grammar since all grammar books include punctuation (at least the ones I've seen).

It's kind of dodgy to claim that something is not grammatically correct because of punctuation, though. The classic example which is often cited is about the Australian animal, the koala.

The koala eats shoot and leaves.

The koala eats, shoots and leaves.

The first sentence describes the diet of the koala. The second sentence, although preposterous, suggests that a koala eats, then shoots something, then leaves (as in departs). Punctuation is certainly important to meaning, but i don't consider it a part of grammar. Your mileage may vary.