He gave the boy an apple改成被动语态,哪一句对a The boy was given an appleb The boy was given an apple by him为什么by him要省略

He gave the boy an apple
改成被动语态,哪一句对
a The boy was given an apple
b The boy was given an apple by him
为什么by him要省略

A是对的.
原句中没有说明是谁给男孩苹果.所以改成被动句后不用加by him

b对