The following sentence has been split into four segments. Identify the segment that contains a grammatical error.
"This smartphone is / superior than / the model I had been / using previously."

Explanation of the Correct Answer:
· The error is in "superior than."
· The word "superior" is an adjective of comparison and does not require "than." Instead, it is followed by "to."
· The correct phrase should be "superior to" instead of "superior than."
Corrected Sentence:
"This smartphone is superior to the model I had been using previously."
Other options:
· (a) "This smartphone is" → Correct; no errors here.
· (b) "using previously" → Correct; "previously" is correctly placed as an adverb.
· (c) "the model I had been" → Correct; past perfect continuous tense is used correctly.
Thus, the correct answer is (d) "superior than" → should be "superior to."