Received a PM asking me to comment on this issue:
Could someone please explain whether "by" in the phrase "by one or more swimmers" is wrong? I read somewhere that "in passive voice use 'by' for actual doers of the axn ".
I am quite confused when to use "of" and when to use"by".
Instructors plz help.
The preposition "by" can be used in multiple ways. You can use by (plus the rest of a prepositional phrase) to indicate whoever is doing an action in a passively-constructed sentence. But "by" can also be used in other ways and does not HAVE to be used to indicate who's doing the passively-constructed action.
The pizza was eaten by me. I am the one doing the action.
The pizza made by Jim was eaten. Jim made the pizza. I don't know who ate it.
The phrase "movements by swimmers" generally indicates that the swimmers are making the movements, so it's not referring directly to the action conveyed by the verb (to synchronize). I would generally say that the movements of one or more is more idiomatic than the movements by one or more, but I don't think that's strong enough in this circumstance. D and E have other, better, ways by which we can eliminate them.
SparpanGamt: Yes, subject-verb agreement is another issue in this problem. The subject and verb agree in both choices C and A.
The subject is "the movements" ("of one or more swimmers" is a prepositional phrase modifier; nothing in there qualifies as the subject). "The movements" is plural so the verb has to be plural. "They synchronize" and "They are synchronized" both work in general (if we're only talking about singular vs. plural).
Then there is also an issue of active vs. passive voice. "The movements" is the subject. Are the movements synchronizing themselves? If so, use active voice. Is something or someone else synchronizing the movements? If so, use passive voice.
The movements can't synchronize themselves, so we can't use active voice (as choice A does). We have to use passive voice (as C does).
