被動語態與主動語態

All the objects tell something about human history,but some can be singled out as prime examples of the ways humans long ago shaped their world.
(1)請教高手幫忙解釋藍色部分的句構分析?("can be singled out"為何不加by +受詞? 還是省略呢?)
(2)另外,如果藍色部分改回來主動語態,該如何寫? 謝謝
更新: All the objects tell something about human history,but some can be singled out as prime examples of the ways humans long ago shaped their world.
(1)"can be singled out"為何不加by +受詞? 還是省略呢?
更新 2: 2)主動語態but we can singled some out as prime examples of the ways that humans long ago shaped their world.
為何不寫but we can singled out some as prime ....?
更新 3: 3.另外原來被動語態but some can be singled out as prime examples of the ways humans long ago shaped their world. 無that
但改成主動語態變成要多that呢
but we can singled some out as prime examples of the ways that humans long ago shaped their world.
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