The first thing that she opens is the door to let them in aha
I just took both AP micro and macro. I don't think any answer would be more appropriate than suppliers and demanders.
C.
The door is made of glass, which is an example of non-porous surface.
Ninhydrin is one of the most widely used reagents for chemical development of fingerprints on porous surfaces.
The correct answer would be C. Hope this helps.