Insert the missing words:

The . . . . . . . . . . . . . . . . . . . . . . . . . means that the whole processmay be at risk where parts of the link are weak or break down. It is only by understanding the whole system that one is able to determine the effect of changes in any one area on other linked areas.

a. variable element

b. random fluctuations

c. series analysis

d. dependency chain