The ReCycle is a bicycle built largely from recycled materials. Identify the following costs connected with the manufacture of the ReCycle bike as variable or fixed:
a. Rubber used in bike tires
b. Recycled aluminum used to make the bike frame
c. Lubricant used on clipless pedal springs
d. Quality inspector's salary
e. Depreciation on equipment used to machine the aluminum in the bike frame
f. Renewable cork used to make the saddle (the seat)
g. Patent on belt drive (used instead of a chain)