2.Which interaction has heavy carriers? Answer (click and hold): Weak (W+, W-, and Z)

3.Which interactions act on the protons in you? Answer (click and hold): All of them

4.Which force carriers cannot be isolated? Why? Answer (click and hold): Gluons, because they carry color charge themselves.

5.Which force carriers have not been observed? Answer (click and hold): Gravitons (Gluons have been observed indirectly.)