a) pressure, temperature
b) vacuum, pressure
c) Thick gauge, thin gauge
d) Temperature, vacuum

Answer: c
Explanation: Thermoforming can be generally classified as Thick gauge and thin gauge thermoforming. Thick gauge thermoforming is a term used for making heavy duty parts, such as- plastic pallets, refrigerator liners, etc. Whereas, thin-gauge thermoforming is the term used to describe the manufacturing of lighter and smaller things, such as disposable cups, containers, trays, lids, and other products for the food, medical, and general retail industries.