Which word correctly completes this sentence? el poncho azul es caro como el sombrero de color oscuro. tanto más tan tantos

The word that correctly completes the sentence is:

- El poncho azul es tan caro como el sombrero de color oscuro.

Explanation:

The translation of the sentence is:

- The blue poncho is as expensive as the dark hat.

In the sentence made, a comparative form called Comparative of Equality is used, in which it is mentioned that a noun is equal to another in a given quality or adjective within it, its Spanish writing format is, in Present, as follows:

Noun + soy/eres/es/somos/son + tan + adjective + como + noun.

As you can see, the only missing part in the sentence would be the word "tan" which is indispensable to form the comparative addressed, the other options are discarded since they would belong to a superiority comparative which in addition to being characterized by having the word "más" requires the word "que" after the adjective.