Option C — Error: then / Correction: to
The correct form is "superior to", as comparatives with Latin-origin adjectives (superior, inferior, senior, junior, prior) always take "to", not "then".
"Then" is used for time/sequence; "than" is used in comparisons — but even "than" is wrong here. Adjectives like superior, inferior, senior, junior are already comparative in form and must be followed by "to", never "than" or "then". Examiners specifically test this rule.