$\rightarrow$ 1. The child may be killed. 

$\rightarrow$ 2. The cat was began beaten by the children.

$\rightarrow$ 3. His house is going to sold by him.

$\rightarrow$ 4. The meeting has to be cancelled.

$\rightarrow$ 5.1 The floor needs to be cleaned. 

      5.2 The floor needs cleaning. 

$\rightarrow$ 6. The floor needn’t be painted.

1. The child may be killed. 

=> May là động từ khiếm khuyết nên may +be+V3/ed

 2. The cat was began beaten by the children.

=> Bị động với thì quá khứ đơn: S+was/were+ V3/ed+ byO

3. His house is going to be sold by him.

=> Cấu trúc: S+am/is/are+ going+to +be+V3/ed+byO

4. The meeting has to be cancelled.

=> Have to là động từ khiếm khuyết nên have to+be+V3/ed

5.1 The floor needs to be cleaned. 

=> Need +to be+ V3/ed cần được làm gì

5.2 The floor needs cleaning. 

6. The floor needn’t be painted

=> Needn't be+ V3/ed: không cần phải làm gì nhưng đã làm rồi