Question

Поставьте глагол-сказуемое во все временные формы Continuous и Perfect в страдательном залоге: The system of secondary education in the United States is known to be a conglomeration of many different kinds of institutions.

Answer 1

Is known
was known
has been known
had been known
will be known
will have been known
В Continuous глагол to know нельзя поставить 

Answer 2

Continuous and Perfect Forms in the Passive Voice

The system of secondary education in the United States is being known to be a conglomeration of many different kinds of institutions. The system of secondary education in the United States has been known to be a conglomeration of many different kinds of institutions. The system of secondary education in the United States was being known to be a conglomeration of many different kinds of institutions. The system of secondary education in the United States had been known to be a conglomeration of many different kinds of institutions. The system of secondary education in the United States will be known to be a conglomeration of many different kinds of institutions. The system of secondary education in the United States will have been known to be a conglomeration of many different kinds of institutions