The cumulative learning curve coefficient CLCC(20, 0.8) is defined as follows: 

a. The cost to produce 20 units in a process with c(1) = 1 and a learning rate of 0.8. 

b. The cost to produce one unit in a process with c(1) = 20 and a learning rate of 0.8. 

c. The cost to produce one unit in a process with c(1) = 1 and a learning rate of 0.8. 

d. The cost to produce the 20th unit in a process with c(1) = 1 and a learning rate of 0.8.