HI Guys
Please do tell me the explainations for these questions. I had tough time getting down these questions.

138.Where once the union had acquiesced to the prejudices 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 Slavs in its ranks.

(A) Where once the union had acquiesced to the prejudices of its English-speaking members by supporting
(B) Where once the union acquiesced to it 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



153. Two week notice being given to employers before leaving a job is the generally accepted protocol.
(A) Two week notice being given to employers before leaving
(B) Giving notice to employers of two weeks before having to leave
(C) Two week’s notice to give to employers before leaving
(D) Giving notice to employers two weeks before leaving
(E) To give two weeks’ worth of notice before having to leave


168. Since the movie was released seventeen UFOs have been sighted in the state, which is more than had been sighted in the past ten years together.
(A) which is more than had been sighted
(B) more than had been sighted
(C) more than they had sighted
(D) more than had reported sightings
(E) which is more than had reported sightings

In the question 138, why do we need to use 'where' instead of 'when' .
In question 168 why is the chioce A wrong.

Thanks
Satya