They are drawing the picture.

→The picture is being drawn by them.

过去进行  was doing → was + being + done

were         were

He was reviewing their lessons at this moment yesterday.

→Their lessons were being reviewed at this moment yesterday.

情态动词  may                      may

can                       can

must                      must

should    do → should + be + done

ought to                   ought to

used to                    used to

You must write an article on the subject.

→An article must be written on the subject.