I / suggest / your factory / fit / new filters to its chimneys / as the dirt and smoke / dangerous.
A.I would suggest that your factory should fit new filters to its chimneys as the dirt and smoke are really dangerous.
B.I would suggest that your factory need to fit new filters to its chimneys as the dirt and smoke are really dangerous.
C.I would suggest that your factory should fit new filters to its chimneys as the dirt and smoke which are really dangerous.
D.I would suggest your factory to fit new filters to its chimneys as the dirt and smoke are really dangerous.