Firstly, meaning of the sentence is:
Although once the union had agreed to impose an alien tax on foreign workers because of pressure from the English speaking union members, after 1897, the union made a sincere effort to enlist Italian workers in their ranks, I.e., abolish tax for the Italian workers.

If we go through the choices, we require had acquiesced because the workers made an effort after 1897, so past perfect is required in the sentence.

This eliminates B and D.

In C and E, in support of and in its supporting of are both incorrect. The union had acquiesced..... By supporting is correct. In support of is inappropriate here. so C and E are also eliminated.

A is correct.

Hope this is correct.

anshulagarwal12 wrote: where once the union had acquiesced to the prejudies of its english speaking members, by supporting the imposition of an alien tax on immigrant workers, after 1897 the United Mine workers made a determined effort to enlist Italians and slaves in its ranks.

a. where once the union had acquiesced to the prejudies of its english speaking members, by supporting
b. where once the union acquiesced to its English-speaking members prejudice for the support of
c. While once the union had acquiesced to the prejudices of its English speaking members in support of
d. While once the union acquiesced to its English speaking members prejudice in supporting
e. While once the union had acquiesced to the prejudices of its English speaking members in its supporting of

IMO use of WHERE is appropriate only for ACTUAL PLACES in gmat and therefore drop A/B.

I see another problem in A esp - the use of PREP PH (BY SUPPORTING...WORKERS). Its not clear what does it modify - whether its modifying HAD ACQUIESCED or MADE. IMO: the way this phrase is placed we can infer that Union had acquiesced to the prejudies by supporting the imposition OR we can also infer The United Mine workers made a determined effort to enlist Italians by supporting the imposition. If this phrase were really modify HAD ACQUIESCED, the best place would be to place it before WHERE...MEMBERS (eg By supporting...workers, where once...members).

D - we need past perfect; drop

C/E - "in support of" is better than "in its supporting of" (presence of ITS suggests that UNION had acquiesced to the prejudices of its English speaking members in UNION'S SUPPORTING of the imposition, but actually we intend to say had acquiesced the prejudices of members in MEMBERS support of the imposition). Presence of 2nd ITS not appropriate. Drop E

IMO C

patanjali.purpose wrote:

anshulagarwal12 wrote: where once the union had acquiesced to the prejudies of its english speaking members, by supporting the imposition of an alien tax on immigrant workers, after 1897 the United Mine workers made a determined effort to enlist Italians and slaves in its ranks.

a. where once the union had acquiesced to the prejudies of its english speaking members, by supporting
b. where once the union acquiesced to its English-speaking members prejudice for the support of
c. While once the union had acquiesced to the prejudices of its English speaking members in support of
d. While once the union acquiesced to its English speaking members prejudice in supporting
e. While once the union had acquiesced to the prejudices of its English speaking members in its supporting of

IMO use of WHERE is appropriate only for ACTUAL PLACES in gmat and therefore drop A/B.

I see another problem in A esp - the use of PREP PH (BY SUPPORTING...WORKERS). Its not clear what does it modify - whether its modifying HAD ACQUIESCED or MADE. IMO: the way this phrase is placed we can infer that Union had acquiesced to the prejudies by supporting the imposition OR we can also infer The United Mine workers made a determined effort to enlist Italians by supporting the imposition. If this phrase were really modify HAD ACQUIESCED, the best place would be to place it before WHERE...MEMBERS (eg By supporting...workers, where once...members).

D - we need past perfect; drop

C/E - "in support of" is better than "in its supporting of" (presence of ITS suggests that UNION had acquiesced to the prejudices of its English speaking members in UNION'S SUPPORTING of the imposition, but actually we intend to say had acquiesced the prejudices of members in MEMBERS support of the imposition). Presence of 2nd ITS not appropriate. Drop E

IMO C

Even I selected 'C' as the answer but the right answer is 'A'. And, the reason I dropped A was that "where" is used for places. Also, in the original sentence, there is no "comma" after members. The original sentence is -
where once the union had acquiesced to the prejudies of its english speaking members by supporting the imposition of an alien tax on immigrant workers, after 1897 the United Mine workers made a determined effort to enlist Italians and slaves in its ranks.

But I still do not understand why are we choosing 'where' over 'while'?

optimist wrote:
Even I selected 'C' as the answer but the right answer is 'A'. And, the reason I dropped A was that "where" is used for places. Also, in the original sentence, there is no "comma" after members. The original sentence is -
where once the union had acquiesced to the prejudies of its english speaking members by supporting the imposition of an alien tax on immigrant workers, after 1897 the United Mine workers made a determined effort to enlist Italians and slaves in its ranks.

But I still do not understand why are we choosing 'where' over 'while'?

I think its not a good question: Different experts have different opinions

https://www.beatthegmat.com/where-vs-whi ... nto-15-645

https://gmatclub.com/forum/where-once-th ... 78602.html