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