Past and Present Participle

The growth of the railroads led to the abolition of local times, which was determined by when the sun reached the oberver's meridian and differing from city to city, and to the establishment of regional times.
(A) which was determined by when the sun reached the oberver's meridian and differing
(B) which was determined by when the sun reached the oberver's meridian and which differed
(C) which were determined by when the sun reached the oberver's meridian and differing
(D) determined by when the sun reached the observer's meridian and differed
(E) determined by when the sun reached the observer's meridian and differing


Explaination:

E) The difference lies in active/passive voice Local times were determined by X, it is the object of X. In other words, "local times" are not determining X but determined by X so past participle is correct. However, local times are differing from city to city because it not only "differed" in the past but it is also "differing" today. We need present participle to logically illustrate that. A, B and C make the second half a relative clause and lack in conciseness compared to the participial forms of D and E A 1972 agreement between Canada and the United States reduced the amount of phosphates that municipalities had been allowed to dump into the Great Lakes. (A) reduced the amount of phosphates that municipalities had been allowed to dump (B) reduced the phosphate amount that municipalities had been dumping (C) reduces the phosphate amount municipalities have been allowed to dump (D) reduced the amount of phosphates that municipalities are allowed to dump (E) reduces the amount of phosphates allowed for dumping by municipalities Explaination: D C,E are out --> 'reduces' is the wrong tense B --> 'phosphate amount' is awkard. Out. A --> Out. Not trying to emphasize two past actions. D. 'are allowed to dump' suggests what the 1972 agreement laid out for the two countries at that specific moment when it was enacted.