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Probelm here appear to be in my grammar knowledge -

the sentence is - Scientists struggling to find ways to prevent cancer have found new hope in the humble grape : a team of researchers at the university of illions found that a compound in grape skins can block the substances that stimulate tumour growth.No error

I spot for the mistake struggling to - but afterwards I see that there is no error - why ? Which is this structure struggling to - I think that must be Scientists were struggling to - past progressive - but Scientists struggling to is not past progressive so than what is ?
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Hello Max

I would take it as a present participle. You can think of it like this:

1. Scientists (who are) struggling to find ways...

MrP
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You have the option to seperate them with commas should you wish but it doesn't look pretty to put commas everywhere.

Moreover they are not going to put commas in your TOEFL test because that would give away the answers easily...

Savvy
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Then is it possible - the baby is crying for an hours - to be paraphrased into the baby crying for an hour - I think it is not possible then why this rule is possible in the previous sentence ? "Scientists struggling to ..... "
Hello MaX

1. The baby was crying for hours.

Here, you have a simple sentence with only one clause. "The baby" is the subject of "was crying". So you can't rephrase it.

2. Scientists struggling to develop a vaccine for bird flu have announced a breakthrough.

Here, you have an embedded clause:

2a. Scientists | struggling to develop a vaccine for bird flu | have announced a breakthrough.

"Scientists" relates both to "struggling" and to "have announced". So you can rephrase it like this:

2b. Scientists | (who are) struggling to develop a vaccine for bird flu | have announced a breakthrough.

MrP
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hm... it seems to be more clear to me but why there is no comma to separate the embedded clause ? in my language we separate them with comma ,
 Savvysavz's reply was promoted to an answer.