Sentence Correction

Most people may not think of photographic processing to be hazardous, but many of the chemicals used can cause health problems, especially if they aren't used in rooms with proper ventilation.

Most people may not think of photographic processing to be hazardous, but many of the chemicals used can cause health problems, especially if they aren't used in rooms with proper ventilation.
Most people may not think of photographic processing being hazardous, but many of the chemicals used can cause health problems, especially if they aren't used in rooms with proper ventilation.
Most people may not think hazardously of photographic processing, but health problems can be caused when many of the chemicals are used in rooms that aren't properly ventilated.
Most people may not think of photographic processing as being hazardous, but many of the chemicals used can cause health problems, especially if they aren't used in rooms with proper ventilation.
Photographic processing, while not thought of as being hazardous, can cause health problems when many of the chemicals used are done so in rooms with no proper ventilation.

Think of... as is the correct idiom.

So, D is the correct choice!!!