I ate a piece of chocolate cake Chuyển đổi

2 câu trả lời

I ate a piece of chocolate cake

=> A piece of chocolate was eaten (by me)

cấu trúc câu bđ thì QKĐ : S + Ved + O=>S + was/were + P2 + by O

I ate a piece of chocolate cake ( câu chủ động)

Chuyển đổi

a piece of chocolate cake was eaten ( câu bị động)

cấu trúc câu bị động thì quá khứ 

S + V-ed + O
She wrote a letter

S + was/were + VpII + (by + O)
A letter was written by her.