How is the pattern of comparative degree?

[Differ]

English Language Tests, Intermediate level

ESL/EFL Test #826 "Comparatives and Superlatives (5)", question 1

This necklace is ......... than the last one you bought me. I'm so lucky to have a rich and generous husband like you!

(a) expensive
(b) more expensive
(c) most expensive

English Language Tests, Intermediate level

ESL/EFL Test #826 "Comparatives and Superlatives (5)", answer 1

This necklace is more expensive than the last one you bought me. I'm so lucky to have a rich and generous husband like you!

Correct answer: (b) more expensive
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how is the pattern of comparative degree

Differ

[Wanderer]

How? How is the pattern? It's fine!!!
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Let my English be checked!