Citing the recent increase in earnings by several computer companies, economists feel that _______________________________________________, especially corporate consumers, are replacing their PCs with more powerful models.

a) a cycle has begun in which personal computer users
b) a cycle for personal computer users has begun in which they
c) there is a cycle beginning for personal computer users
d) it is the beginning of a cycle for personal computer users
e) personal computer users are in the beginning of a cycle when they

The example provided here would best be accomplished and completed by option A, i.e. "a cycle has begun in which personal computer users". The other options exemplify either inappropriate context that does not support the previous claim or contain grammatical errors. For example in option B, pronoun "they" has no referent, while the last option displays an incorrect logical predication and option C and D depicts a confused or unclear assertion. Thus, this makes us conclude with option A as the answer as it best fits the passage both grammatically and logically.