Choose the sentence that corrects the shift of voice in the following sentence. this is the sentence he could not remember if the bathroom door had been locked by him from the inside. and the answers
a. it could not be remembered if he had locked the bathroom door from the inside
b. it could not be remembered by him if he had locked the bathroom door from the inside
c. he could not remember if the bathroom door was locked from the inside. or
d. e could not remember if he had locked the bathroom door from the inside.