The author here is describing, in a sequential or chronological way, a series of events that took place in the past (hence the use of the past tense), namely: 1) "...he finally convinced...", 2) "Early results were not..." and 3) "...but... customers became hooked."
Answer:
D) In a command economy, individuals have less economic freedom.
Text structure. Organization, vocabulary, and content all contribute to the way the text is formatted. The fluency could also be counted as content.