In sentences like "All he can think of is this moment," all is taking singular is. However, in sentences where there is more than one subject, does all still take singular is?
All he can hear is the wind, the sound of the rain, and the thunder.
All that's present at the end of the hall is the storage and another room.
Do both these sentences take "all...is"? Could this be explained with a grammatical rule? In these sentences, is all referring back to predicate nominatives?