As a result of record low temperatures, the water pipes on the third floor froze, which caused the heads of the sprinkler system to burst, which released torrents of water into offices on the second floor.
- As a result of record low temperatures, the water pipes on the third floor froze,
The sentence starts by presenting the result of an event. It says that in some place, because of the unusually low temperatures, the water in the pipes on a certain floor of a building froze.
- which caused the heads of the sprinkler system to burst,
This part presents the result of the event mentioned earlier. It tells us that because of the resulting pressure from the freezing of the water in the pipes, the water-sprinklers burst. Reading further:
- which released torrents of water into offices on the second floor.
Finally, we get to know of another event in the series. We find out that the bursting of the sprinklers forcefully released a lot of water in the offices situated on the floor beneath the one on which the pipes were located.
To sum up, the sentence presents a chain of effects caused by a particular event. First, the unusually low temperatures in a certain place led to the freezing of water in the pipes on a certain floor in a building. This event caused the water sprinklers to burst, forcefully dispensing a huge amount of water in the offices on the floor beneath.
Both the instances of the relative pronoun modifiers which are incorrect in the sentence. The sentence intends to present the results of two particular actions. But it uses noun modifier which for both the purposes. Because neither of the instances of which in the sentence has a corresponding noun entity to modify, the sentence has modifier errors.
One of the ways to rectify this error is to use comma + verb-ing modifier to present the result of the preceding action. For instance, the relevant portion of the sentence can be written as:
… the water pipes on the third floor froze, causing the heads of the sprinkler system to burst,
This choice has the errors pointed out in the error analysis.
In this choice, the relative pronoun modifier which has been used in two instances, and in both these instances, which has been incorrectly used to modify the action of freezing.
1. Modifier Error
This choice repeats the modifier error of choice A by repeating the first usage of which.
2. Structure Error
The independent clause (IC) …torrents of water were then released… is connected to the preceding IC …the water pipes… froze… just by a comma. This structure is ungrammatical. Two ICs must be joined with comma + FANBOYS.
This choice employs the comma + verb-ing modifiers causing… and …then releasing…. Use of the first comma + verb-ing modifier …causing… is correct because it correctly modifies the action of the preceding clause and also makes sense with the subject of the modified clause the water pipes on the third floor. Per this modification, the water pipes on a certain floor froze, and this action caused the heads of the sprinkler to burst.
However, use of the second comma + verb-ing modifier then releasing is not correct as the modification illogically conveys that because the water pipes froze, torrents of water were released. From the meaning analysis we know that water was released because the sprinklers burst.
This indeed is the correct answer choice. While the comma + verb-ing modifier …causing… correctly presents the result of water pipes freezing, the two parallel actions …to burst and (to) release… clearly convey that the sprinklers burst and dispensed water because the water pipes froze.