为什么:They picked up some rocks and put (them)in the spacesship,为什么要用them呢?

为什么:They picked up some rocks and put (them)in the spacesship,为什么要用them呢?
为什么:They picked up some rocks and put (them)in the spacesship,为什么要用them呢?

为什么:They picked up some rocks and put (them)in the spacesship,为什么要用them呢?
them 是宾语代指rocks

them 代的是rocks