时态正确;recent修饰extended sales slump
had been发生在said之前,用过去完成时态ok
The perfect tenses, though used infrequently on the GMAT, often induce this type of confusion. Remember, the present perfect is used when an event began at some time in the past and continues to the present moment, while the past perfect indicates a completed past event that happened before a second completed past event. In the cited example, the verb "said" in the non-underlined section of the sentence is a past tense verb. In order to indicate that the sales slump occurred prior to this past announcement, the past perfect tense is necessary. A second approach would have been to focus on the recent/recently split. It is nonsensical that a retailer would INTENTIONALLY extend a sales slump. However, this is exactly what is suggested by the adverb "recently," which modifies the adjective "extended." The sentence should instead include the adjective "recent," which correctly describes the slump. Thus, answer choices B and C are eliminated. From there, the its/their pronoun split is relatively straightforward. Since the subject of the sentence is the singular "retailer," the singular pronoun "its" is correct.
主句中的 seven-store retailer said it would start a three-month liquidation sale in all of its stores. 提示前面的单数代词和过去完成时态
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