The teacher is explaining new rules.
The teacher explained new rules.
The teacher has already explained new rules.
The teacher had explained new rules.
The teacher was explaining new rules.
The rules were explained by the teacher.
new rules are being explained by the teacher.
new rules were being explained by...
... will be explained by...
...has been explained by...
the teacher will have explained new rules
new rules will have been explained
the teacher has been explaining new rules
the teacher had been explaining new rules
NOTE: Present( Past) Perfect Continuous почти не используется в страдательном залоге