`C_1`: It is said that China dug up the ocean floor to build artificial islands.

`C_2`: China is said to have dug up the ocean floor to build artificial islands.

`@` Câu bị động kép:

`+` C1: It + is/was + V3/ed + that + S + V

`+` C2: `S_2` + is/was + V3/ed + toV-inf (cùng thì)

                                                + to have V3/ed (khác thì)

`-` Cùng thì:

`-` HTĐ `-` HTĐ

`-` QKĐ `-` QKĐ

`-` HTĐ `-` TLĐ

`-` Khác thì:

`-` HTĐ `-` QKĐ

`-` QKĐ `-` QKHT