Choose the correct form of the verb to complete these sentences from a postcard with the past participle. De repente, se ____ el cielo y empezó a llover a cántaros.

The subject is “el cielo,” which is singular, so the auxiliary verb must be “había.” In compound tenses formed with “haber,” the past participle stays unchanged, giving “se había abierto el cielo” (“the sky had opened”).

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