1. The darts contained a drug that put the wolves to sleep.
Can I also use "which" to take place of "that" in this sentence?
Plus, what about using "which" to take place of "that" in these sentences:
2. Few kids in the survey met the guidelines for physical activity that raises the heart rate and makes you breathe harder.
3. Pi came to an island that is sweet by day but dangerous by night.
4. Other major effects have included programs to destroy rabbit holes or use viruses that sicken and kill rabbits.
5. The answer is probably as simple as the fact that people change.
Honestly, I am quite doubtful about the last sentence, for the "that" in it seems unchangeable.
Anybody help?
Best Answer
In sentences 1-4 you have integrated relatives (often called "restrictive"), the sort that isn't surrounded by commas. You can tell these are relative clauses because they have gaps—specifically, their subjects are missing.
The gap in each case is left behind by the relative pronoun which. But in your examples, you've replaced these relative pronouns with that. You can undo this change and put which back in its rightful spot, if you like:
If these were supplementary relatives (often called "non-restrictive"), the sort that's usually surrounded by commas, you wouldn't be able to replace which with that; you'd be stuck with which in each case.
In sentence 5 you have something very different! The clause following that is complete and therefore contains no gap. And without a gap, there's no place for a relative pronoun like which. The word that, therefore, cannot be taking the place of which; there's no substitution to undo, because which wasn't there in the first place.
Instead, this particular that is a subordinator, introducing a subordinate finite clause:
Since this isn't a relative clause, the relative pronoun which has no place here. Since which isn't an option, you're stuck with that in this example.