помогите перевести в Active Voice или Passive Voise

Перевод Odissara грамотный, только я бы перед словом "учитель" везде определённый артикль употребила. А вот у ROACH Bug в последнем предложении неверна видо-временная форма глагола, там нужен Present Perfect, а не Past Simple
The teacher explains a new material every lesson.
A new material is explained by the teacher every lesson.
The teacher is explaining a new material now.
A new material is being explained by the teacher now.
The teacher has already explained a new material.
A new material has been explained by the teacher this week

A teacher explains a new material every lesson.
A new material is explained by a teacher every lesson.
Now the teacher is explaining a new material.
A new material is being explained by the teacher now.
The teacher has already explained a new material.
A new material has been explained by the teacher this week.

Удачи!

Ребята, слово "material" в значении "учебный материал" - неисчисляемое сущ-е.
Уберите везде артикль "а" перед "new material", там никакой артикль не нужен.

The teacher explains a new material every lesson.
A new material is explained by teacher every lesson.
Now the teacher is explaining a new materil.
A new material is being explained by the teacher now.
The teacher has already explained a new material.
A new material was explained by the teacher last week.