Consider the following:1.Aerosols2.Foam agents3.Fire retardants4.Lubricants In the making ofhow many of the above are hydrofluorocarbons used?

1. A

   Only one

   Only one. HFCs appear in more than one of the listed uses.

2. B

   Only two

   Only two. Aerosols, foam blowing and fire suppression all use HFCs.

3. C

   Only three

   Only three. Aerosols, foam agents and fire retardants / suppression. Lubricants are not an HFC use-class here.

4. D

   All four

   All four. Lubricants are oils, not HFC applications in this listing.

Summary. Official key is (c) only three. Hydrofluorocarbons replaced CFCs in aerosols, foam blowing and some fire-extinguishing systems. They are refrigerants too. They are not used as lubricants, so four is too many.