请教大全925、440、551

925 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

(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

答案A。Where 到底是指代哪个的？怎么看不懂意思？

440 It is an oversimplified view of cattle raising to say that all one has to do with cattle is leave them alone while they feed themselves, corral them, and to drive them to market when the time is ripe.

(A) all one has to do with cattle is leave them alone while they feed themselves, corral them, and to

(B) all one has to do with cattle is to leave them alone to feed themselves, to corral them, and

答案是C。不明白，to do is to do啊，leave怎么可以原型放在is后面？

551 Once positioned in space, the Hubble Space Telescope will capture light from sources twenty times fainter compared to those that can be detected by ground-based instruments.

(D) than those that can be detected

答案D。fainter 指的是sources？