As to which is the independent clause, what if we rephrase that first portion of the sentence to say "Francis Perkins investigations were dogged and her lobbying was persistent." Does that not seem to be a sentence? Is this not what the first part of the sentence is saying (in a convoluted way)?

It is not clear to me that the last portion is the main clause of this sentence seeing that it begins with "that." For example, what if this sentence was "I told you that Alfred E. Smith and Franklin D. Roosevelt recruited Perkins to work within the government, rather than as a social worker." Now it is clear that "I told you" is the main sentence.

In that spirit, rearrange the first part of the sentence to say, "Frances Perkins' investigations of the garment industry were so dogged that..." That first portion would be the main stem of the sentence. Yes this verb requires an explanation of exactly what happened but this does not mean that it is not the main stem of the sentence.

In that case how to explain the underlined portion? This seems to be a parallel extension of that main sentence, although without the verb "were" which means that this is a modifier between the commas, but one that parallels the main sentence.

Try this addition to my earlier example, "SO powerful were his arms, and thick his legs, that he easily lifted the weight." Basically the modifier here needs to be almost like a reserve player for a sports team. If the main clause is removed this modifier is so alike in form that it could just take the place. In my example it could be "So thick were his legs that he easily lifted the weight."

Does that help?

Clock 60 -

That is the strange thing about this question. Everyone is expecting an 'And' here. Including me!!

I really wanted to see ""So dogged were Frances Perkins' investigations of the garment industry AND so persistent WAS her lobbying for wage and hour reform that..."

This would really show that the parallelism is necessary. But is it too clear? Did they do this to make it more obscure? Clearly it must be acceptable. This is an official GMAT question and E is the OA. I checked to make sure this was not mistyped and it was not. This is the question.

Here is the story - in my example above I made the elements truly parallel with the "AND" but in that case I need to add the verb "WAS" to the underlined portion to make these exactly parallel. Because the comma creates a modifier we get by without the "Was" and without the "and" but we still must have a parallel structure of these elements.

It is an unusual sentence!

@David

Thanks again for your post and it really helped, but still have some doubts in my mind.

Doubt 1:-- regarding independent clause

I understood what you said about the main stem..completely agree..no problem, but If m correct a sentence must contain at least one independent clause...m i right?? if so then in this question, for OA E, should we say that

So dogged were Frances Perkins'investigations of the garment industry that Alfred E. Smith and Franklin D. Roosevelt recruited Perkins to work within the government, rather than as a social worker.

This whole bunch is an independent clause....??? m i right???

because "So dogged were Frances Perkins'investigations of the garment industry" as you suggested, this can be the main stem but i don't think it can be an independent clause as it lacks a complete meaning or a finishing...m i right???

Doubt 2:-- Regarding parallelism

David, why i'm asking this question again is because this clause and modifier thing...this is the first question out of all i solved so far where we are talking about the parallelism in terms of structure b/w a clause and modifier...but i think the way you express your thought, with an example, i should accept it...but seems surprising to me...

My doubt is what type of Modifier this is??? what name we give to this phrase???

Please clear, and thanks again for your effort to make me understand one of the toughest problem i have seen...

Regards
Atul