They have to do their duty every year.

→ Their duty has to be done every year.

The mechanic has just repaired the engine.

→ The engine has just been repaired by the mechanic.

These boys laughed at the teacher.

→ The teacher was laughed at by these boys.

The teacher is translating this sentence into Vietnamese.

→ This sentence is being translated into Vietnamese by the teacher.

The little boy is carrying the bag for the old man.

→ The bag is being carried for the old man by the little boy.

We brought some new books to the class this morning.

→ Some new books were brought to the class by us this morning.

They planted big trees here.

→ Big trees were planted here.

People often wash hands before meals.

→ Hands are often washed before meals.

Her grandmother sewed her many new clothes.

→ She was sewn many new clothes by her grandmother.

Her son's absence makes her worried.

→ She is worried about her son's absence.