Student or Learner
I wonder if the nouns in the following sentences are in the plural or in the singular .
1. The two students took their life/lives after the school massacre.
2. Both Sarah and Jim have lived all their life/lives in Florida.
3. They sharpened their knife/knives.
I think in the first and second one, though we are talking about two states of being alive, life should be used, because everyone has one life and in #3, knives is the key because people can have more than one knife.